FORMULABANK

Used to find the area of a triangle.
$\mathrm{Perimeter}=a+b+c$

$s=\frac{1}{2}\cdot \left(\mathrm{Perimeter}\right)$

$\mathrm{Area}=\sqrt{s\cdot (s-a)\cdot (s-b)\cdot (s-c)}$

Example:
Works only for triangles.

$s=\frac{1}{2}\cdot 12,99=6,495$

$\sqrt{6,495\cdot (6,495-3,16)\cdot (6,495-4)\cdot (6,495-5,83)}\approx 5,99$