If A, B, C are nonzero matrices, show by a counterexample that AB = AC does not imply that B = C.

I'm not too worried about this.

Under what extra conditions would you be able to conclude that

B = C?

Don't know what I could do here.

Maybe A,B,C invertible?

I know that finding a counterexample will give me this answer, but I'm going to bed soon and will do it when I wake up. Thanks