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Date May 2021 Marks available 4 Reference code 21M.2.SL.TZ1.8
Level Standard Level Paper Paper 2 Time zone Time zone 1
Command term Show that Question number 8 Adapted from N/A

Question

Two straight fences meet at point AA and a field lies between them.

A horse is tied to a post, PP, by a rope of length rr metres. Point DD is on one fence and point EE is on the other, such that PD=PE=PA=rPD=PE=PA=r and DˆPE=θDˆPE=θ radians. This is shown in the following diagram.

The length of the arc DEDE shown in the diagram is 28m28m.

A new fence is to be constructed between points BB and CC which will enclose the field, as shown in the following diagram.

Point CC is due west of BB and AC=800mAC=800m . The bearing of BB from AA is 195°195°.

Write down an expression for rr in terms of θθ.

[1]
a.

Show that the area of the field that the horse can reach is 392θ2(θ+sinθ)392θ2(θ+sinθ).

[4]
b.

The area of field that the horse can reach is 460m2460m2. Find the value of θθ.

[2]
c.

Hence, find the size of DˆAEDˆAE.

[2]
d.

Find the size of AˆBCAˆBC.

[2]
e.i.

Find the length of new fence required.

[3]
e.ii.

Markscheme

r=28θr=28θ           A1

 

[1 mark]

a.

recognising sum of area of sector and area of triangle required           (M1)

12r2θ+12r×r×sin(π-θ) (=r22(θ+sin(π-θ))12r2θ+12r×r×sin(πθ) (=r22(θ+sin(πθ))           A1

sin(π-θ)=sinθsin(πθ)=sinθ (substitution seen anywhere)           A1

12(28θ)2θ+12(28θ)2sinθ  OR  12(28θ)2(θ+sinθ)           A1

area=392θ2(θ+sinθ)           AG

 

[4 marks]

b.

392θ2(θ+sinθ)=460           (M1)

θ=1.43917

θ=1.44           A1

 

[2 marks]

c.

π-(π-θ)2  OR  θ2           (M1)

DˆAE=0.719588

DˆAE=0.720           A1

 

[2 marks]

d.

AˆBC=195-180+90           (A1)

=105°           A1

 

[2 marks]

e.i.

choosing sine rule          (M1)

BCsin DˆAE=800sin105  OR  BCsin DˆAE=800sin1.83          A1

BC=546(m)           A1

 

[2 marks]

e.ii.

Examiners report

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d.
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e.i.
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e.ii.

Syllabus sections

Topic 3— Geometry and trigonometry » SL 3.2—2d and 3d trig, sine rule, cosine rule, area
Show 133 related questions
Topic 3— Geometry and trigonometry » SL 3.4—Circle: radians, arcs, sectors
Topic 3— Geometry and trigonometry

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