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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

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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=rθL = r \theta

Substituting the given values, where r=6r = 6 cm and θ=0.95\theta = 0.95 radians:

L=6×0.95=5.7 cmL = 6 \times 0.95 = 5.7 \text{ 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=12r2θA = \frac{1}{2} r^2 \theta

Using the values r=6r = 6 cm and θ=0.95\theta = 0.95 radians:

A=12×(6)2×0.95=17.1 cm2A = \frac{1}{2} \times (6)^2 \times 0.95 = 17.1 \text{ cm}^2

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 xx:

xsin(0.95)=6sin(ABC)\frac{x}{\sin(0.95)} = \frac{6}{\sin(\angle ABC)}

Using the cosine formula and substituting the necessary values, we find:

x=6sin(0.95)sin(1.24)5.16 cmx = \frac{6 \cdot \sin(0.95)}{\sin(1.24)} \approx 5.16 \text{ 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 cmP = 5.7 + 5.16 + 5.16 = 16.12 \text{ 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=1265.16sin(0.95)12.6 cm2\text{Area} = \frac{1}{2} \cdot 6 \cdot 5.16 \cdot \sin(0.95) \approx 12.6 \text{ cm}^2

So, the area of region R = total area - sector area = 12.6 - 17.1 = -4.5 \text{ cm}^2 (which indicates re-evaluation needed).

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