Question

Find the area of an equilateral triangle (regular 3-gon) with the given measurement 9-inch A=sq. in.

Answer 1

Assuming is a 9 inch side.

$\bf \textit{area of an equilateral triangle}\\\\ A=\cfrac{s^2\sqrt{3}}{4}\qquad \begin{cases} s=length~of\\ \qquad a~side\\ -------\\ s=9 \end{cases}\implies A=\cfrac{9^2\sqrt{3}}{4}\implies A=\cfrac{81\sqrt{3}}{4}$