1, calculate the radius.

2 calculate the sector area

Three MINUS one.

Radius solution: let the radius be x (ah ~ so complicated)

Then, the radius times the angle is the arc length.

So x times angle = arc length ①.

The distance between two points of the new moon is a.

Then there is also an equation between a and X.

A is generally the radius multiplied by the cosine of the half angle ②.

Answer.

Know how to cut?