The inverse of the matrix is the matrix assuming ad − bc ≠ 0. Also, the inverse of the bilinear function (a.k.a. Möbius transformation) is the function again assuming ad − bc ≠ 0. The elementary takeaway is that here are two useful equations that are similar in appearance, so memorizing one makes it easy to memorize […] The post Inverting matrices and bilinear functions first appeared on John D. Cook.
