Heron's formula for the area of a triangle

Given a triangle with sides $a,b$ and $c$ Heron's formula is:

$A=\sqrt{p\cdot (p-a)\cdot (p-b)\cdot (p-c)}$

where $p$ is the semiperimeter:

$p={\displaystyle \frac{a+b+c}{2}}$

It works when all the sides of a triangle are known we can calculate the area with no need to know the height.