Hey guys, I'm currently completing a Finite Element course and there is a tricky integral that we use to evaluate forces in a 3-point triangle. I was hoping someone would know how to explain the general result,

 \int_A L_1^p L_2^q L_3^r dA = \frac{2A p! q! r!}{(p+q+r+2)!}

Where, p, q and r are constants. A represents the total area of a 3 sided triangle and,

 L_1 = \frac{ A_1}{A}

 L_2 = \frac{ A_2}{A}

 L_3 = \frac{ A_3}{A}

 A_1, A_2, and A_3 represent the divided areas of the triangle when we are looking at a point. For example, say we have a 3-sided triangle and point P is smack dab in the middle. If we draw lines from the 3 points that connect the triangle to the point of interest, the triangle will be divided into 3 areas. Those represent  A_1, A_2, and A_3 .

In essense the Ls represent the area coordinates of our point of interest.

I'm thinking there may be some geometry involved here?! It actually doesn't matter because all we need is the general result for our computations, but I would like to know! hehe.