Hi,

I think the answer you are looking for is Area= absin(Θ) where a is the length of the long side and b is the length of the short side and Θ is the included angle.

The way you derive this is to break up the parallelogram into two right triangles and a square and calculate the areas of each of the three figures ( the right triangles each have the same area) and add them up. Hint the height of the triangles is bsin(Θ) and he base is bcos(Θ) so the area of one of the triangles is 1/2b sin(Θ) cos(Θ)

This should get you started let me know if you need any more help.

Jim Stanton