okay so i set it up as a 2x4 matrix:
dM1/dx1 dM1/dx2 dM1/dx3 dM1/dx4
dM2/dx1 dM2/dx2 dM2/dx3 dM2/dx4
but from there i got confused. for example in the first one, how do i take the partial derivative of (x1+x2)/(x3+x4) with respect to x1? wouldn't it be like 1/0 ? then where does the point (1,1,1,1) come into play? ah i'm so confused..