Area of the polygon with  equal sides is .

Divide the polygon into congruent triangles with central angle .

The polygon is inscribed in circle with radius .

Therefore, two sides of the triangle have equal length of .

Determine area of the each triangle.

Area of each triangle is .

Here and .

Total polygon area is times the area of the single triangle.

.

(b) Find .

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Assume .

As , then .

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Property of limit function: .

(a) .

(b) .