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July 2nd, 2013, 08:23 PM   #1
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Trigonometry - I don't understand the solution

http://i.imgur.com/vYqr0X5.jpg

Area of half a circle is (pi*r^2)/2

What happened to pi?

phi - sin(phi) ????
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July 2nd, 2013, 08:38 PM   #2
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Re: Trigonometry - I don't understand the solution

What they have done to find the area of the shaded portion is to take the area of the circular sector, and subtracted the area of the isosceles triangle.

The are of the circular sector is:



The area of the triangle is:



Hence:

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