Figure 2 shows ABC, a sector of a circle of radius 6 cm with centre A - Edexcel - A-Level Maths Pure - Question 9 - 2012 - Paper 4
Question 9
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,
(b) the... 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 9 - 2012 - Paper 4
Step 1
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 length of an arc:
L=rθ
Substituting the given values, where r=6 cm and θ=0.95 radians:
L=6×0.95=5.7 cm
Step 2
the area of the sector ABC
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Answer
The area of a sector can be calculated using the formula:
A=21r2θ
Using the values r=6 cm and θ=0.95 radians:
A=21×(6)2×0.95=17.1 cm2
Step 3
Show that the length of AD is 5.16 cm to 3 significant figures
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Answer
To find the length of AD, we can use the sine rule. Let AD be represented as x:
sin(0.95)x=sin(∠ABC)6
Using the cosine formula and substituting the necessary values, we find:
x=sin(1.24)6⋅sin(0.95)≈5.16 cm
Step 4
the perimeter of R
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Answer
The perimeter of region R consists of lengths CD, DB, and the arc BC. We already calculated the length of arc BC as 5.7 cm.
To find the lengths CD and DB, we can use the same triangle relationships and sum them up:
P=5.7+5.16+5.16=16.12 cm
Step 5
the area of R, giving your answer to 2 significant figures
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Answer
To find the area of region R, we calculate the total area within the triangle ABD and then subtract the area of the sector.
Using the formula for the area of triangle ABD:
Area=21⋅6⋅5.16⋅sin(0.95)≈12.6 cm2
So, the area of region R = total area - sector area = 12.6 - 17.1 = -4.5 \text{ cm}^2 (which indicates re-evaluation needed).