# Area of a Regular Polygon 3

__Area of a regular polygon of n sides when the radius r of the circumscribed circle is given__

Let be the radius of the circumscribed circle.

the area of the polygon area of

But the area of

Also, the perimeter of the polygon

But

Also

Perimeter

Or (As)

__Example__:

A regular decagon is inscribed in a circle, the radius of which is. Find the area of the decagon.

__Solution__:

Here , __ __

The area of the decagon

The area of the decagon square cm.