Scroll down for a solution to this problem.
The orange area is 1.
Since it’s a quarter circle, the angle between the radii is right. From Thales we know that the line connecting the end points of those radii must be a diagonal of the unit circle. Using the Pythagorean theorem, we can find the radius to be √2.
An orange quarter of moon
That comes out very soon
The moon is orange and glowed
It looks like fire that burned
Playing and hiding with the clouds
The moon is a quarter, not perfectly round
All the days passes so easy
The orange moon makes me happy !!