Figure 2 shows $ABC$, a sector of a circle of radius 6 cm with centre $A$ - Edexcel - A-Level Maths Pure - Question 8 - 2012 - Paper 4
Question 8
Figure 2 shows $ABC$, a sector of a circle of radius 6 cm with centre $A$. Given that the size of angle $BAC$ is 0.95 radians, find
(a) the length of the arc $BC$, ... show full transcript
Worked Solution & Example Answer:Figure 2 shows $ABC$, a sector of a circle of radius 6 cm with centre $A$ - Edexcel - A-Level Maths Pure - Question 8 - 2012 - Paper 4
Step 1
Find the length of the arc $BC$
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Answer
To find the length of the arc BC, we use the formula for the arc length:
extArcLength=rheta
where r is the radius and θ is the angle in radians. Thus,
BC=6imes0.95=5.7 cm.
Step 2
Find the area of the sector $ABC$
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Answer
To find the area of the sector, we use the formula:
extArea=21r2θ
Substituting in the values gives us:
Area=21×62×0.95=17.1 cm2.
Step 3
Show that the length of $AD$ is 5.16 cm to 3 significant figures
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Answer
We need to express the triangle relations. Since angle BAC=0.95 radians,
Using the sine rule:
sin(0.95)AD=sin(θ)6
Finding AD involves using the side opposite the angle.
After calculating, we find:
AD=sin(1.24)6⋅sin(0.95)=5.16 cm.
Step 4
Find the perimeter of $R$
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Answer
The perimeter P of region R can be found by adding the lengths of lines CD, DB, and arc BC:
Using values:
P=AD+AB+BC=5.16+6+5.7=16.86 cm.
Step 5
Find the area of $R$, giving your answer to 2 significant figures
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Answer
To find the area of the region R, we need the area of triangle ABD and the area of sector ABC:
Area of ABA=21⋅5.16⋅6⋅sin(0.95)=12.6 cm2.
Then, area of region R = Area of sector ABC - Area of triangle ABD: