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Voronoi Diagrams

Practice exam-style IB Math AI questions for Voronoi Diagrams, aligned with the syllabus and grouped by topic.

Verified by Karim
Verified by Karim
Paper
Difficulty
Status
Level
Question 1
SL • Paper 1
Easy
Calculator Permitted
SL • Paper 1
Easy
Calculator Permitted

Two emergency call stations are located at A(2,3)A(2,3) and B(8,7)B(8,7) on a coordinate map. A Voronoi edge between their service regions lies on the perpendicular bisector of ABAB.

A

Find the midpoint of ABAB and the gradient of ABAB.

[2]
B

Find the equation of the Voronoi edge in the form ax+by+d=0ax+by+d=0, where a,b,dZa,b,d\in\mathbb Z.

[2]
C

State the relationship between the distances from a point on this edge to AA and to BB.

[1]
Question 2
SL • Paper 1
Easy
Calculator Permitted
SL • Paper 1
Easy
Calculator Permitted

Two health clinics are located at C(2,6)C(2,6) and D(8,6)D(8,6). Their service regions are separated by a Voronoi edge.

A

Determine the equation of the Voronoi edge.

[2]
B

A house is located at P(3.5,9)P(3.5,9). State which clinic is nearer to the house and justify your answer.

[2]
Question 3
SL • Paper 1
Easy
Calculator Permitted
SL • Paper 1
Easy
Calculator Permitted

A Voronoi diagram shows three bicycle repair stations AA, BB and CC. Point PP lies inside the cell containing AA, point QQ lies on the edge separating the cells of AA and BB, and point RR is a vertex where the three cells meet. The displayed edges are portions of unbounded rays and continue beyond the boundary of the plotting window.

Voronoi diagram with three stations and query points; each displayed edge extends to the plotting-window boundary.
A

State the repair station nearest to PP.

[1]
B

Describe the relationship between the distances QAQA and QBQB.

[1]
C

Describe the relationship between RARA, RBRB and RCRC.

[1]
D

State what a Voronoi cell represents in this context.

[1]
Question 4
SL • Paper 1
Medium
Calculator Permitted
SL • Paper 1
Medium
Calculator Permitted

Three weather stations have coordinates and recorded rainfall as shown.

StationCoordinatesRainfall (mm)
AA(1,2)(1,2)4242
BB(6,3)(6,3)5555
CC(4,8)(4,8)6161

Nearest-neighbour interpolation is used to estimate rainfall at P(5,5)P(5,5).

A

Calculate the distance from PP to each weather station.

[3]
B

Estimate the rainfall at PP.

[1]
C

State one limitation of using nearest-neighbour interpolation in this context.

[1]
Question 5
SL • Paper 1
Medium
Calculator Permitted
SL • Paper 1
Medium
Calculator Permitted

A rectangular nature reserve is modelled by 0x80\leq x\leq8 and 0y80\leq y\leq8, where one unit represents 1 km1\ \text{km}. Monitoring sites are located at A(2,3)A(2,3), B(6,3)B(6,3) and C(2,7)C(2,7). Within the reserve, the Voronoi cell of AA is bounded by the reserve boundary and the perpendicular bisectors of ABAB and ACAC.

A

Find the equations of the perpendicular bisectors of ABAB and ACAC.

[2]
B

Describe the cell containing AA using inequalities.

[1]
C

Calculate the area of the cell containing AA.

[2]
Question 6
SL • Paper 1
Medium
Calculator Permitted
SL • Paper 1
Medium
Calculator Permitted

A regional authority must locate a waste facility as far as possible from its nearest protected habitat. Two candidate Voronoi vertices are V(4,3)V(4,3) and W(7,5)W(7,5). The nearest habitat to VV is at A(1,1)A(1,1), and the nearest habitat to WW is at B(10,2)B(10,2).

A

Calculate the distance from VV to its nearest habitat.

[2]
B

Calculate the distance from WW to its nearest habitat.

[2]
C

Determine which candidate should be selected.

[1]
Question 7
SL • Paper 1
Medium
Calculator Permitted
SL • Paper 1
Medium
Calculator Permitted

Two delivery depots are located at A(0,0)A(0,0) and B(8,0)B(8,0). A new depot is added at C(4,6)C(4,6). Two sides of the new Voronoi cell lie on the perpendicular bisectors of ACAC and BCBC.

A

Find the equation of the perpendicular bisector of ACAC.

[2]
B

Find the equation of the perpendicular bisector of BCBC.

[2]
C

Find the point of intersection of these two perpendicular bisectors.

[2]
Question 8
SL • Paper 1
Medium
Calculator Permitted
SL • Paper 1
Medium
Calculator Permitted

A Voronoi edge separating two sites AA and BB has equation y=x+6y=-x+6. Site BB has coordinates (5,4)(5,4).

A

Find the equation of the line through AA and BB.

[2]
B

Find the midpoint of ABAB.

[2]
C

Find the coordinates of site AA.

[2]
Question 9
HL • Paper 1
Medium
Calculator Permitted
HL • Paper 1
Medium
Calculator Permitted

A bounded Voronoi cell for a wildlife monitoring station has vertices (1,1)(1,1), (6,1)(6,1), (7,4)(7,4), (4,7)(4,7) and (1,5)(1,5), listed in order around the cell. One coordinate unit represents 1 km1\ \text{km}. The estimated animal density throughout the cell is 1818 animals per square kilometre.

Bounded Voronoi cell with five vertices in cyclic order.
A

Calculate the area of the Voronoi cell.

[4]
B

Estimate the number of animals in this cell.

[2]
Question 10
HL • Paper 1
Medium
Calculator Permitted
HL • Paper 1
Medium
Calculator Permitted

Existing service centres are located at A(0,0)A(0,0) and B(10,0)B(10,0). A new centre is added at N(5,4)N(5,4). Its new Voronoi cell is determined in part by the perpendicular bisectors of ANAN and BNBN.

A

Find the equation of the perpendicular bisector of ANAN.

[2]
B

Find the equation of the perpendicular bisector of BNBN.

[2]
C

Determine whether P(3,2)P(3,2) belongs to the new centre's Voronoi cell. Justify your answer.

[2]
Question 11
HL • Paper 1
Medium
Calculator Permitted
HL • Paper 1
Medium
Calculator Permitted

A proposed facility must maximize its distance from the nearest settlement. The only candidate locations are Voronoi vertices V1(4,3)V_1(4,3), V2(8,6)V_2(8,6) and V3(5,9)V_3(5,9). A nearest settlement to each vertex is respectively A(1,1)A(1,1), B(11,2)B(11,2) and C(2,11)C(2,11).

A

Calculate the nearest-settlement distance for each candidate.

[3]
B

Determine where the facility should be located.

[2]
C

Explain why the distance to the nearest settlement, rather than the distance to every settlement, is used for this decision.

[1]
Question 12
HL • Paper 1
Medium
Calculator Permitted
HL • Paper 1
Medium
Calculator Permitted

Air-quality sensors A(2,2)A(2,2), B(6,2)B(6,2) and C(10,2)C(10,2) record pollution indices 1414, 2020 and 1717, respectively. Nearest-neighbour interpolation is used along the horizontal route y=2y=2, for 0x120\leq x\leq12.

A

Find the two points on the route where the nearest-neighbour estimate changes.

[2]
B

Write down the nearest-neighbour estimate I(x)I(x) along the route, excluding the two boundary points.

[2]
C

Calculate the mean estimated pollution index over the whole route.

[2]
Question 13
HL • Paper 1
Medium
Calculator Permitted
HL • Paper 1
Medium
Calculator Permitted

Three communication towers are located at A(0,0)A(0,0), B(6,2)B(6,2) and C(2,8)C(2,8). A Voronoi vertex VV is equidistant from all three towers.

A

Find the equation of the perpendicular bisector of ABAB.

[2]
B

Find the equation of the perpendicular bisector of ACAC.

[2]
C

Determine the coordinates of VV.

[2]
D

Calculate the common distance from VV to the three towers.

[1]
Question 14
HL • Paper 1
Medium
Calculator Permitted
HL • Paper 1
Medium
Calculator Permitted

The Voronoi edge separating sites AA and BB has equation 2xy3=02x-y-3=0. Site BB is located at (8,2)(8,2).

A

Find the equation of the line containing AA and BB.

[2]
B

Find the midpoint of ABAB.

[2]
C

Find the coordinates of AA.

[2]
Question 15
HL • Paper 1
Medium
Calculator Permitted
HL • Paper 1
Medium
Calculator Permitted

Four sites are located at A(3,0)A(-3,0), B(3,0)B(3,0), C(0,4)C(0,4) and D(0,6)D(0,-6). The perpendicular bisector of ABAB is the line x=0x=0. Only part of this line is a Voronoi edge because sites CC and DD cut it off.

A

For a point P(0,y)P(0,y), write expressions for PA2PA^2, PC2PC^2 and PD2PD^2.

[3]
B

Find the values of yy for which PP is no farther from AA and BB than it is from either CC or DD.

[3]
C

State the Voronoi edge shared by the cells of AA and BB.

[1]
Question 16
HL • Paper 1
Medium
Calculator Permitted
HL • Paper 1
Medium
Calculator Permitted

An existing Voronoi diagram has sites A(0,0)A(0,0), B(8,0)B(8,0) and C(4,8)C(4,8). Its three cells meet at N(4,3)N(4,3). A new site is added at the point NN.

A

Verify that NN is equidistant from AA, BB and CC.

[2]
B

Find the equation of the perpendicular bisector of the segment joining the new site NN to AA.

[2]
C

Explain which of the three existing Voronoi cells are affected by adding the new site.

[2]
Question 17
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

Two mobile libraries are located at A(1,2)A(1,2) and B(7,6)B(7,6). The boundary between their service regions is the perpendicular bisector of ABAB. A second straight line has equation y=x1y=x-1.

Coordinate-plane map of the two library sites, the perpendicular-bisector line, the second straight line, and their intersection point.
A
I.

Find the midpoint of ABAB and the gradient of ABAB.

[2]
II.

Hence find the equation of the perpendicular bisector of ABAB, giving your answer in the form ax+by=cax+by=c, where aa, bb and cc are integers.

[3]
B
I.

Find the coordinates of the intersection point of the two lines.

[2]
II.

A resident lives at P(5,3)P(5,3). Determine which of AA or BB is closer to PP. Justify your answer using distances.

[2]
Question 18
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

Three soil-moisture stations have the following coordinates and readings. Nearest-neighbour interpolation is used along the path y=5y=5, for 0x80\leq x\leq8.

StationCoordinatesMoisture index
AA(0,1)(0,1)2828
BB(6,1)(6,1)4444
CC(3,7)(3,7)6565
Stations, path y=5, and Voronoi boundaries.
A
AI.

Find the value of xx at which the line y=5y=5 meets the perpendicular bisector of ACAC, and state whether this point lies on the specified path.

[2]
AII.

Find the value of xx where the path crosses the perpendicular bisector of BCBC.

[3]
B
BI.

Write down the nearest-neighbour moisture estimate along each section of the path, excluding boundary points.

[2]
BII.

Calculate the mean estimated moisture index along the path.

[2]
Question 19
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

A square wildlife reserve is modelled by 0x100\leq x\leq10 and 0y100\leq y\leq10, where one unit represents 1 km1\ \text{km}. A ranger station is at R(3,3)R(3,3). Its neighbouring stations are at E(7,3)E(7,3), N(3,7)N(3,7) and S(0,0)S(0,0).

Square reserve with stations and Voronoi cell of R.
A
I.

Find the perpendicular bisectors of RERE, RNRN and RSRS.

[3]
II.

Write inequalities describing the Voronoi cell containing RR.

[2]
B
I.

Calculate the area of the cell containing RR.

[3]
II.

The estimated animal density throughout this cell is 1212 animals per square kilometre. Estimate the number of animals in the cell.

[2]
Question 20
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

A regional authority must locate a hazardous-material store as far as possible from its nearest conservation site. Three candidate locations are V1(3,4)V_1(3,4), V2(8,3)V_2(8,3) and V3(6,8)V_3(6,8). The nearest conservation sites to these locations are C(2,5)C(2,5), B(10,7)B(10,7) and B(10,7)B(10,7), respectively.

Coordinate map of the three candidate locations, the conservation sites, and the river $y=0$.
A
I.

Calculate the distance from each candidate vertex to its nearest conservation site.

[3]
II.

Identify all candidates that maximize the distance to the nearest conservation site.

[2]
B
I.

The river is represented by y=0y=0. Of the optimal candidates, determine which is farther from the river.

[2]
II.

Explain why candidate locations, rather than the conservation sites, are considered as possible locations.

[1]
Question 21
SL • Paper 2
Medium
Calculator Permitted
SL • Paper 2
Medium
Calculator Permitted

A bounded Voronoi cell for a rainfall gauge has vertices (1,2)(1,2), (5,1)(5,1), (8,4)(8,4), (6,8)(6,8) and (2,7)(2,7), listed in order. One coordinate unit represents 1 km1\ \text{km}. The gauge records rainfall of 72 mm72\ \text{mm}.

Voronoi cell for rainfall gauge.
A
I.

Use the shoelace formula to calculate the area of the cell.

[3]
II.

State the rainfall estimate at every point strictly inside this cell when nearest-neighbour interpolation is used.

[2]
B
I.

Estimate the total volume of rainfall falling on the cell, in cubic metres.

[3]
II.

State one limitation of this estimate.

[1]
Question 22
HL • Paper 3
Medium
Calculator Permitted
HL • Paper 3
Medium
Calculator Permitted

Four marine monitoring stations have Voronoi-cell areas and recorded water temperatures as shown. Nearest-neighbour interpolation assigns each point in a cell the temperature at its station.

Station

Voronoi-cell area / km2\mathrm{km^2}

Recorded temperature / C^\circ\text{C}

A

18

14

B

25

17

C

31

20

D

26

16

A
I.

Verify that the total surveyed area is 100 km2100\ \text{km}^2.

[2]
II.

Calculate the area-weighted mean estimated temperature.

[2]
B

A station with temperature 20C20^\circ\text{C} has its cell reduced from 3131 to 24 km224\ \text{km}^2 when a new station is added. State the area transferred from the old cell.

[2]
C

Discuss one limitation of nearest-neighbour interpolation for estimating sea temperature.

[2]
Question 23
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

Four charging stations are located at (2,2)(2,2), (8,2)(8,2), (8,8)(8,8) and (2,8)(2,8). A fifth station NN is added at (5,5)(5,5).

Four stations at the corners of a square and station N at the centre, with the Voronoi cell outline shown.
A
I.

Find the equations of the perpendicular bisectors between NN and each of the four existing stations.

[4]
II.

Read the four vertices of the Voronoi cell containing NN from the diagram.

[2]
B
I.

Calculate the area of the new station's Voronoi cell.

[2]
II.

Explain why all four original cells lose the same area when NN is added.

[2]
Question 24
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

A Voronoi edge between two archaeological survey sites has equation y=2x+1y=2x+1. One of the sites is A(2,7)A(2,7), and the other site is BB.

Coordinate plane showing the Voronoi edge with sites A and P.
A
I.

Find the equation of the line containing AA and BB.

[2]
II.

Find the midpoint of ABAB.

[3]
B
I.

Hence find the coordinates of BB.

[2]
II.

Determine whether P(4,9)P(4,9) is closer to AA than to BB.

[2]
Question 25
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

Three flood-response hubs are located at A(2,1)A(-2,1), B(4,3)B(4,3) and C(1,7)C(1,7). Their Voronoi cells meet at a vertex VV.

Coordinate map of hubs A, B, C, incident Q, and the perpendicular bisectors.
A
I.

Find the equations of the perpendicular bisectors of ABAB and ACAC.

[4]
II.

Hence find the coordinates of VV.

[2]
B
I.

Calculate the common distance from VV to the three hubs.

[2]
II.

An incident occurs at Q(0,5)Q(0,5). Determine the nearest response hub.

[2]
Question 26
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

Three protected nesting sites are located at A(1,1)A(1,1), B(9,1)B(9,1) and C(4,8)C(4,8). A candidate wind turbine location VV is the Voronoi vertex equidistant from these sites. A second candidate WW has nearest-site distance 5.105.10 units.

Map of sites A, B, C and candidate points V and W.
A
I.

Find the equations of the perpendicular bisectors of ABAB and ACAC.

[3]
II.

Hence find the coordinates of VV.

[3]
B
I.

Calculate the nearest-site distance at VV.

[2]
II.

Determine which candidate should be chosen to maximize the distance from the nearest nesting site. Justify your answer.

[2]
Question 27
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

A rectangular agricultural district has area 120 km2120\ \text{km}^2 and is divided into three regions, one associated with each sensor. The region associated with sensor AA has vertices (0,0)(0,0), (5,0)(5,0), (6,4)(6,4), (3,7)(3,7) and (0,6)(0,6), listed in order. The region associated with sensor BB has area 41 km241\ \text{km}^2. Sensors AA, BB and CC record crop indices 1212, 2020 and 3232, respectively. For this question, each region is assigned the crop index recorded by its associated sensor.

Given rectangular district, region A boundary, and sensor sites; no nearest-sensor partition is implied.
A
I.

Calculate the area of the region associated with AA.

[3]
II.

Hence find the area of the region associated with CC.

[2]
B
I.

Using this constant-per-region interpolation, calculate the mean estimated crop index over the district.

[3]
II.

Explain why this model produces sudden changes in the estimated crop index at boundaries between regions.

[2]
Question 28
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

A chemical-storage facility must be placed as far as possible from its nearest residential area. Candidate VV is the intersection of the lines 2x+y=112x+y=11 and x2y=1x-2y=-1. Two other candidates are W(8,5)W(8,5) and U(5,9)U(5,9). Nearest residential sites to VV, WW and UU are A(1,0)A(1,0), B(11,2)B(11,2) and C(2,7)C(2,7), respectively.

Planning map of the known candidate points and residential sites.
A
I.

Find the coordinates of VV.

[2]
II.

Calculate the nearest-residential-site distance for each candidate.

[3]
B
I.

Determine the preferred candidate using the maximin criterion.

[2]
II.

Candidate WW is later excluded because it lies in a flood zone. Determine the next preferred candidate and explain why.

[2]
Question 29
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

A rectangular forest is modelled by 0x120\leq x\leq12 and 0y120\leq y\leq12, where one coordinate unit represents 1 km1\ \text{km}. Ranger stations are located at A(2,2)A(2,2), B(10,2)B(10,2) and C(6,10)C(6,10). Nearest-station regions are modelled using a Voronoi diagram.

Forest boundary with ranger stations and hiker point.
A
I.

Find the equations of the perpendicular bisectors of ABAB and ACAC.

[2]
II.

Hence find the Voronoi vertex and its distance from each station.

[2]
B

The cell containing AA is bounded by x=0x=0, y=0y=0, x=6x=6 and y=12x+8y=-\frac12x+8. Calculate its area.

[2]
C

A hiker is at P(7,6)P(7,6). Determine the station assigned to the hiker and justify your answer.

[2]
Question 30
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

Initially, sensors AA, BB and CC are at positions x=0x=0, x=7x=7 and x=13x=13 and record moisture indices 1212, 2020 and 88, respectively. Nearest-neighbour interpolation is used along the channel. The data for sensor NN, to be installed in part b, are shown in the table but are not used initially.

Sensor or boundary

Position x [km]

Moisture index

A

0

12

B

7

20

N (part b)

9

16

C

13

8

Channel end

16

Not applicable

A
I.

Find the positions where the nearest-neighbour estimate changes.

[2]
II.

Calculate the mean estimated moisture index over the whole channel.

[2]
B

A new sensor NN is installed at x=9x=9 and records an index of 1616. Find the interval assigned to NN.

[2]
C

Show that adding NN does not change the mean estimated index over the channel.

[2]
Question 31
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

Four emergency beacons are located at the corners A(1,1)A(1,1), B(9,1)B(9,1), C(9,9)C(9,9) and D(1,9)D(1,9) of a square region. A fifth beacon is added at N(5,5)N(5,5).

Square region with four corner beacons and a central beacon.
A
I.

Find the perpendicular bisectors of NANA and NBNB.

[2]
II.

Using symmetry, write down the other two boundaries of the cell containing NN.

[2]
B

Find the vertices and area of the cell containing NN.

[2]
C

State which original cells are changed when NN is added, and explain why.

[2]
Question 32
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

A conservation authority must locate a chemical-storage site as far as possible from the nearest protected habitat. Three internal Voronoi vertices are V(4,5)V(4,5), W(9,4)W(9,4) and U(7,9)U(7,9). The protected habitat points considered are A(1,1)A(1,1), B(12,0)B(12,0) and C(7,3)C(7,3). For each candidate, the nearest-habitat distance is the distance to the closest of these three points.

Candidate locations, protected habitat points, entrance, and restricted zone.
A
I.

Calculate the nearest-habitat distance for each candidate.

[2]
II.

Determine the preferred location under the authority's criterion.

[2]
B

A restricted zone is the circle with centre (8,8)(8,8) and radius 22. Determine whether the preferred location is permitted.

[2]
C

The remaining candidates are VV and WW. The authority chooses the candidate with the greater nearest-habitat distance; if tied, it chooses the tied candidate nearer the entrance at (0,0)(0,0). Determine the final location.

[2]
Question 33
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

The bounded Voronoi cell of an ecological sampling site has vertices (1,1)(1,1), (7,1)(7,1), (8,4)(8,4), (5,8)(5,8) and (1,6)(1,6), listed in order. One coordinate unit represents 1 km1\ \text{km}. Nearest-neighbour interpolation assigns a density of 2424 nesting pairs per square kilometre throughout the cell.

Pentagonal Voronoi cell with labelled vertices and an interior sampling site.
A
I.

Calculate the area of the cell.

[2]
II.

Estimate the number of nesting pairs in the cell.

[2]
B

A new site removes 6.5 km26.5\ \text{km}^2 from this cell. Calculate the revised estimate, assuming the density assigned to the remaining cell is unchanged.

[2]
C

Explain why the estimate of 900900 should not be interpreted as an exact count.

[2]
Question 34
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

Disease-monitoring sites are at A(0,0)A(0,0), B(8,0)B(8,0) and C(0,6)C(0,6) and record infection indices 66, 1414 and 1010, respectively. Their Voronoi cells meet at VV.

Coordinate map showing the three disease-monitoring sites and their recorded infection indices.
A
I.

Find the coordinates of VV.

[2]
II.

Verify that VV is equidistant from the three sites.

[2]
B

Explain why nearest-neighbour interpolation does not give a unique infection index at VV.

[2]
C

A researcher assigns the arithmetic mean of tied readings at a Voronoi vertex. Find the assigned index and discuss whether this remains nearest-neighbour interpolation.

[2]
Question 35
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

A noise-generating facility must be positioned as far as possible from the nearest residential site. Three admissible internal Voronoi vertices and their distances to the nearest residence are shown in the table.

Vertex

Coordinates

Nearest-residence distance [km]

P

(3, 8)

5.40

Q

(9, 7)

6.10

R

(6, 12)

6.10

A
I.

Identify all candidates that maximize the distance to the nearest residence.

[2]
II.

A power connection is at (12,12)(12,12). Determine which maximizing candidate is nearer the connection.

[2]
B

State the final choice if distance from residences is the primary criterion and connection distance is used only to break a tie.

[2]
C

Explain why choosing the point with the greatest average distance from all residences could give a different result.

[2]
Question 36
HL • Paper 3
Hard
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HL • Paper 3
Hard
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A missing rescue post SS has a Voronoi edge with post A(0,2)A(0,2) on the line x=3x=3. It also has a Voronoi edge with post B(6,10)B(6,10) on the line y=6y=6.

Coordinate diagram with posts A, B, and P, plus the candidate perpendicular bisectors $x=3$ and $y=6$. The displayed full lines are supporting lines and are not necessarily complete Voronoi edges.
A
I.

Use the edge x=3x=3 to determine SS.

[2]
II.

Verify that y=6y=6 is the perpendicular bisector of SBSB.

[2]
B

Point P(5,4)P(5,4) lies between the two given edges. Determine whether PP is nearer to SS than to both AA and BB.

[2]
C

Explain why the full lines x=3x=3 and y=6y=6 need not both appear as complete edges in the final Voronoi diagram.

[2]
Question 37
HL • Paper 2
Hard
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HL • Paper 2
Hard
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A research station S(4,4)S(4,4) has neighbouring stations A(0,2)A(0,2), B(8,2)B(8,2), C(7,8)C(7,8) and D(1,8)D(1,8). Its Voronoi cell is bounded by the perpendicular bisectors between SS and these four sites.

Voronoi cell for S, neighbouring stations, and the sample rectangle.
A
I.

Show that the cell containing SS is described by the inequalities
2x+y7,2xy9,6x+8y81,6x+8y332x+y\geq7,\quad 2x-y\leq9,\quad 6x+8y\leq81,\quad -6x+8y\leq33

[4]
II.

Find the coordinates of the four vertices of the cell.

[2]
B
I.

Calculate the area of the Voronoi cell.

[3]
II.

A sample point is chosen uniformly from the rectangle 0x80\leq x\leq8, 1y8-1\leq y\leq8. Find the probability that it lies in the cell containing SS.

[3]
Question 38
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

Two existing data centres are at A(0,0)A(0,0) and B(10,0)B(10,0). A third centre is placed at N(t,6)N(t,6), where 0<t<100<t<10. The perpendicular bisectors of ABAB and ANAN meet at VV.

Fixed centres A and B, with N moving along y=6.
A
I.

Show that the coordinates of VV are
V(5,t210t+3612)V\left(5,\frac{t^2-10t+36}{12}\right)

[3]
II.

Find the values of tt for which VV lies on the line y=2y=2.

[2]
B
I.

Find the value of tt for which the distance from VV to AA is minimized.

[3]
II.

Calculate this minimum distance.

[2]
Question 39
HL • Paper 2
Hard
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HL • Paper 2
Hard
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A rectangular delivery region is modelled by 0x100\leq x\leq10 and 0y80\leq y\leq8. Existing depots are at A(0,0)A(0,0), B(10,0)B(10,0) and C(4,9)C(4,9). A new depot is added at N(4,3)N(4,3).

Coordinate diagram of the delivery region, depots A, B, C and N, and the boundary of N's Voronoi cell. Render with a true equal data-unit aspect ratio, so one x-unit equals one y-unit, while keeping labels readable and showing C(4,9).
A
I.

Find inequalities representing points that are at least as close to NN as to each of AA, BB and CC.

[3]
II.

Find the vertices of the new Voronoi cell after it is clipped by the rectangular boundary.

[3]
B
I.

Calculate the area of the new Voronoi cell.

[3]
II.

A customer is chosen uniformly at random from the delivery region. Find the probability that the new depot is the customer's nearest depot.

[3]
Question 40
HL • Paper 2
Hard
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HL • Paper 2
Hard
Calculator Permitted

The Voronoi edge between an unknown monitoring site SS and site A(0,0)A(0,0) has equation x+2y=5x+2y=5. The edge between SS and site B(8,2)B(8,2) is claimed to have equation y=3x12y=3x-12.

Sites A and B with the two Voronoi edge lines.
A
I.

Find the equation of the line containing AA and SS.

[2]
II.

Hence find the coordinates of SS.

[4]
B
I.

Verify that y=3x12y=3x-12 is the perpendicular bisector of SBSB.

[3]
II.

Find the vertex where the two stated Voronoi edges intersect.

[1]
Question 41
HL • Paper 2
Hard
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HL • Paper 2
Hard
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Two ferry terminals are at A(2,2)A(2,2) and B(10,6)B(10,6). Their ordinary Euclidean Voronoi edge crosses a straight coastal road with equation y=1y=1. A passenger terminal is proposed at P(7,1)P(7,1).

Two ferry terminals, their Voronoi edge, coastal road y=1, and proposed terminal P.
A
I.

Find the equation of the perpendicular bisector of ABAB.

[4]
II.

Find the point where this edge crosses the coastal road.

[2]
B
I.

Using Euclidean distance, determine which ferry terminal is nearer to PP.

[2]
II.

The road network requires passengers to travel only horizontally or vertically. Under this rule, the travel distances from PP to AA and BB are 72+12|7-2|+|1-2| and 710+16|7-10|+|1-6|, respectively. Determine the nearer terminal and evaluate the suitability of the Euclidean Voronoi model.

[2]
Question 42
HL • Paper 3
Hard
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HL • Paper 3
Hard
Calculator Permitted

A Voronoi edge separating archaeological survey sites AA and BB lies on 3x+4y25=03x+4y-25=0. Site BB is located at (9,7)(9,7).

Voronoi edge 3x+4y-25=0 with site B at (9,7).
A
I.

Find the coordinates of the midpoint MM of ABAB.

[2]
II.

Hence determine the coordinates of AA.

[2]
B

Determine which of AA and BB is closer to P(4,4)P(4,4).

[2]
C

Explain why reflecting BB in the line containing the Voronoi edge produces AA.

[2]
Question 43
HL • Paper 3
Hard
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HL • Paper 3
Hard
Calculator Permitted

A city compares ordinary Euclidean distance with Manhattan distance, defined by d=x2x1+y2y1d=|x_2-x_1|+|y_2-y_1|. Two depots are at A(2,2)A(2,2) and B(8,6)B(8,6).

Coordinate map showing depots A, B and comparison point P.
A
I.

On the line y=4y=4, find the point equidistant from AA and BB using Manhattan distance.

[2]
II.

On the line x=5x=5, find the point equidistant from AA and BB using Manhattan distance.

[2]
B

For P(4,5)P(4,5), compare its assignments under Manhattan and Euclidean distance.

[2]
C

Explain why the two metrics can produce different Voronoi cells in this context.

[2]
Question 44
HL • Paper 3
Hard
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HL • Paper 3
Hard
Calculator Permitted

Two coastal transmitters are located at A(0,0)A(0,0) and B(12,0)B(12,0). A third transmitter is located at N(6,t)N(6,t), where t>0t>0. The three Voronoi cells meet at VV.

Feature

Data

Note

A

(0,0)

fixed transmitter

B

(12,0)

fixed transmitter

Midpoint of AB

(6,0)

halfway between A and B

N

(6,t), t > 0

third transmitter

V

equidistant from A, B and N

Voronoi vertex

Coastal region condition

6 ≤ t ≤ 12

used in part (c)

A
I.

Explain why VV has xx-coordinate 66.

[2]
II.

Show that V=(6,t2362t)V=\left(6,\frac{t^2-36}{2t}\right).

[2]
B

Determine the values of tt for which VV lies on or above the xx-axis.

[2]
C

The coastal region requires 6t126\leq t\leq12. Determine the greatest possible common distance from VV to the three transmitters.

[2]
Question 45
HL • Paper 3
Hard
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HL • Paper 3
Hard
Calculator Permitted

Delivery hubs are located at L(0,0)L(0,0), R(14,0)R(14,0) and N(7,6)N(7,6). A vehicle travels east along the horizontal road y=hy=h from x=0x=0 to x=14x=14 at constant speed.

Voronoi hubs L, R, N with bisectors.
A
I.

Find the perpendicular bisectors of LNLN and RNRN.

[2]
II.

Show that the length of road inside the cell of NN is 12h+137\frac{12h+13}{7}, assuming the road intersects both boundaries of the cell of NN within 0x140\le x\le14; equivalently, 1312h8512-\frac{13}{12}\le h\le\frac{85}{12}.

[2]
B

The vehicle spends 25%25\% of its journey in the cell of NN. Determine hh.

[2]
C

Explain why the percentage of travel time equals the percentage of route length in this model.

[2]
Question 46
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

Warehouses are located at the corners A(0,0)A(0,0), B(16,0)B(16,0), C(16,12)C(16,12) and D(0,12)D(0,12) of a rectangular industrial zone. A new warehouse is added at N(8,6)N(8,6).

Coordinate diagram of the rectangular industrial zone with the four corner warehouses and the new warehouse.
A
I.

Find the perpendicular bisectors of NANA and NBNB.

[2]
II.

Write inequalities describing the side of each boundary containing NN.

[2]
B

Determine whether P(7,2)P(7,2) can belong to the new cell by testing these two inequalities.

[2]
C

Explain why satisfying only these two inequalities is insufficient to prove that PP is in the cell of NN.

[2]
Question 47
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

At an unsampled location PP, the nearest environmental station is AA, with reading 1818. If PP is inserted as a temporary site, it takes fractions 0.200.20, 0.500.50 and 0.300.30 of its new cell from stations AA, BB and CC, whose readings are 1818, 2424 and 1515. A natural-neighbour estimate uses these fractions as weights.

A schematic Voronoi diagram showing a newly inserted point P and the portions of its new cell taken from three neighbouring station cells.
A
I.

Verify that the three fractions form valid interpolation weights.

[2]
II.

Calculate the natural-neighbour estimate at PP.

[2]
B

State the nearest-neighbour estimate at PP and compare it with the natural-neighbour estimate.

[2]
C

Explain why natural-neighbour interpolation can produce a smoother model than nearest-neighbour interpolation.

[2]
Question 48
HL • Paper 3
Hard
Calculator Permitted
HL • Paper 3
Hard
Calculator Permitted

A fixed communications site is at A(0,0)A(0,0). A second site moves along the line y=4y=4 and has coordinates B(t,4)B(t,4), where t>0t>0. The perpendicular bisector of ABAB meets the positive xx-axis at XX.

Coordinate diagram showing fixed site A, moving site B on y = 4, and the perpendicular bisector meeting the positive x-axis at X for t = 6.
A
I.

Show that the perpendicular bisector has equation 2tx+8y=t2+162tx+8y=t^2+16.

[2]
II.

Hence show that the xx-coordinate of XX is t2+8t\frac{t}{2}+\frac{8}{t}.

[2]
B

Determine the value of tt for which XX is closest to the origin.

[2]
C

Find the minimum possible distance OXOX and interpret this result in terms of the moving site.

[2]

Vectors