Draw a regular pentagon and construct a square with area equal to the area of the pentagon.Also draw regular hexagon ,heptagon,octagon and their respective squares with area to the polygons.

(Note:- Figure should be used only for reference as the length of the sides are not exactly 3 cm)

$$\begin{gathered} \mathrm{Now} \mathrm{as} \mathrm{we} \mathrm{know} \mathrm{that} \mathrm{area} \mathrm{of} \mathrm{a} \mathrm{regular} \mathrm{pentagon} \mathrm{is} \\ A=\frac{1}{4}\sqrt{5(5+2\sqrt{5})}{a}^2 \mathrm{where} a \mathrm{is} \mathrm{the} \mathrm{length} \mathrm{of} \mathrm{each} \mathrm{side} \\ \mathrm{Here} \mathrm{we} \mathrm{have} \mathrm{taken} a=3 cm \\ \mathrm{Hence} A=\frac{1}{4}\sqrt{5(5+2\sqrt{5})} \times 3cm\times 3cm=\frac{9}{4}\times 6.8819 c{m}^2\approx 15.48 c{m}^2 \\ \mathrm{Now} \mathrm{length} \mathrm{of} \mathrm{each} \mathrm{side} \mathrm{of} \mathrm{the} \mathrm{square} = \sqrt{15.48 c{m}^2}=3.93 cm \end{gathered}$$


(Note:- Figure should be used only for reference as the length of the sides are not exactly 3.93 cm)