1. The problem statement, all variables and given/known data L = lambda. Prove: d(A^-1)/dL = -(A^-1)(dA/dL)(A^-1) 2. Relevant equations ??? 3. The attempt at a solution I did this as an analogy with function of numbers, but don't know how to extend this to matricies. for example: lets say A = f(L) d(f(L)^-1)/dL = - (f(L)^-2*d(f(L))/dL = -(A^-1)*dA/dL*(A^-1) But what is the matrix form?