I am studying for finals and am looking over previous problems that I missed significant points on. My instructor doesn't comment on why things are incorrect and he doesn't discuss homework, so I am on my own to figure out why I am wrong. Anyway, I would like some help figuring out where I went wrong.
Theorem:
If matrices such that , then are invertible. Furthermore, we have
Problem:
Show that if then
Proof:
By the theorem above we have
Which doesn't seem to get me anywhere. Any help is appreciated. Thank you in advance.