Heron's formula

In geometry, Heron's formula (or Hero's formula) gives the area of a triangle in terms of the three side lengths ⁠${\displaystyle a,}$⁠ ⁠${\displaystyle b,}$⁠ ⁠${\displaystyle c.}$⁠ Letting ⁠${\displaystyle s}$⁠ be the semiperimeter of the triangle, ${\displaystyle s={\tfrac {1}{2}}(a+b+c),}$ the area ⁠${\displaystyle A}$⁠ is

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

It is named after first-century engineer Heron of Alexandria (or Hero) who proved it in his work Metrica, though it was probably known centuries earlier.