Area of an equilateral triangle of side a units can be calculated by using the formula $(s-a)\sqrt{s(s-a)}$.

Concept: If a triangle has three sides, a, b, and c, semi-perimeter s, and area of triangle A, then the semi-perimeter and area of the triangle are given as:

$\mathrm{s}=\frac{\mathrm{a}+\mathrm{b}+\mathrm{c}}{2}$

$\text{A}=\sqrt{\text{s}(\text{s}-\text{a})(\text{s}-\text{b})(\text{s}-\text{c})}$

In an equilateral triangle, $\mathrm{a}=\mathrm{b}=\mathrm{c}$

By Heron's formula,

Area of the given equilateral triangle $=\sqrt{s(s-a)(s-a)(s-a)}$

$\Rightarrow (s-a)\sqrt{s(s-a)}$

Hence, the given statement is true.