When the triangle's height is not given or cannot be found easily, then which of the following formula can be used to find the triangle's area?

Heron's formula is,

Area of a triangle = $\sqrt{s(s-a)(s-b)(s-c)}$ 

where s is the semi-perimeter and a,b and c are the sides of the triangle.

So, we can use Heron's formula when the height of the triangle is not given or cannot be found easily.