Heron's Formula

Theorem
Given a triangle $$\triangle ABC$$ with sides $$a$$, $$b$$, and $$c$$ opposite points $$A$$, $$B$$, and $$C$$, respectively.

Let $$s$$ be the semiperimeter, so $$s = \frac{a + b + c}{2}$$.

Then the area $$A$$ of the triangle is given by the formula $$A = \sqrt{s(s - a)(s - b)(s - c)}$$.