Area of Triangles

If you know the base and the height of the triangle, use the formula:  Area = 1/2 · base · height.

If you know two sides of the triangle and the size of the included angle, use the formula:  

     Area = 1/2 · a · b · sin(C).

If you know the lengths of the three sides of the triangle, first find the semiperimeter:  s = (a + b + c) / 2,

then use the formula:  Area  =  √( s · (s - a) · (s - b) ·(s - c) ).