3. Multiplication and Inverse Matrices
I've been multiplying matrices already, but certainly time for me to discuss the rules for matrix multiplication. And the interesting part is the many ways you can do it, and they all give the same answer. And they're all important. So matrix multiplication, and then, come inverses. So we mentioned the inverse of a matrix. That's a big deal. Lots to do about inverses and how to find them. Okay, so I'll begin with how to multiply two matrices. First way, okay, so suppose I have a matrix A multiplying a matrix B and -- giving me a result -- well, I could call it C. A times B. Okay. So, let me just review the rule for this entry. That's the entry in row i and column j. So that's the i j entry. Right there is C i j. We always write the row number and then the column number. So I might -- I might -- maybe I take it C 3 4, just to make it specific. So instead of i j, let me use numbers. C 3 4. So where does that come from, the three four entry? It comes ...