__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.

Area of the polygon area of

But Area of

Also, 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 , __ __

Area of decagon

Area of decagon Square cm