Triangle inscribed in two squares

Geometry Level 2

This area of the circle is π \pi and the area of triangle O F G OFG is 0.25 0.25 .

What is the measure of A O F \angle AOF in degrees?


The answer is 60.

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1 solution

Since the circle's area equals π \pi , the radius must be 1. Now let's call the angle FOG 2 α 2\alpha . The area of the blue triangle can be written as function of α \alpha . The height of the triangle equals c o s ( α ) cos(\alpha) and the base equals 2 s i n ( α ) 2sin(\alpha) . Now the area of the blue triangle is: 1 2 2 s i n ( α ) c o s ( α ) = 1 2 s i n ( 2 α ) = 0.25 \frac{1} {2}\cdot 2sin(\alpha)cos(\alpha)= \frac{1} {2}\cdot sin(2\alpha) = 0.25 . So s i n ( 2 α ) = 0.5 sin(2\alpha) = 0.5 and 2 α = 30 2\alpha = 30 . This leads to A O F = 90 30 = 60 \angle AOF = 90 - 30 = 60 .

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