Heron's formula

Heron's formula is used to find the area of scalene triangle using the lengths of its sides and its perimeter.

The formula is:

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

$a,b,c$ are the side lengths and $s$ is half of the perimeter of the triangle. $s=(a+b+c)/2$

It is named after first-century engineer Hero of Alexandria, who proved it in his work Metrica.