Question

what is heron's formula?

Answer 1

heron's formula is to get are of scalene triangle[√ (s)(s - a)(s-b)(s-c) 
where s is semi-perimeter (half of the total perimeter of the triangle )
a, b,c are the lengths of the three sides of the triangle.

Answer 2

where a,b,c are sides of triangle.
S=semiperimeter=a+b+c/2

$\sqrt{S(S-a)*(S-b)*(S-c)}$