A=g×h2
Right triangle: A = a*b/2
Equilateral triangle: A =
Isosceles triangle: A=12×ah
For all the other triangles, you basically have to find a height and multiply it by one of the sides of a triangle.
In this case, the height(h) is multiplied by the side (b) and their product divided by 2.
A = b*h/2