Derive the formula for the area of a triangle.?

Forget about trig for a second. Draw a rectangle. Note that it's area is base*height. Now cut it on a diagonal. You end up with 2 identical triangles. The area of each is 1/2 base*height. You have proven that area of a right triangle is 1/2 base*height. Now draw a non-right triangle. Can you extend the idea and prove that the area of this triangle is also 1/2 base*height?