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s344n2d4d5 [400]
3 years ago
6

What is the area of the sector ?​

Mathematics
1 answer:
worty [1.4K]3 years ago
8 0

They forget to say "not to scale".  I'm guessing this is trig because I don't see another way to do it.

Let's consider x=chord PQ first.  By the Law of Cosines

x^2 = 3^2 + 5^2 - 2(3)(5) \cos 81^\circ = 34 - 30\cos 81^\circ

We have an isosceles triangle formed by two radii of 9 cm and x=PQ.  By the Law of Cosines again,

x^2 = 9^2 + 9^2 - 2(9)(9) \cos B

x^2 = 162 - 162 \cos B

\cos B = \dfrac{162 - x^2}{162} = 1 - \dfrac{x^2}{162}

\cos B = 1 - \dfrac{34 - 30\cos 81^\circ}{162}

B = \arccos \left(1 - \dfrac{34 - 30\cos 81^\circ }{162} \right)

The area of the circle is the fraction given by the angle,

A = \dfrac{B}{360^\circ} \pi r ^2

A \approx \dfrac{ \arccos \left(1 - \dfrac{34 - 30\cos 81^\circ}{162} \right) }{360} (3.142)9^2

A\approx 24.7474332960707

Answer: 24.7 sq cm

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