Hey Stormey.
Recall that det(AB) = det(A)*det(B) for operators A and B.
we didn't learn determinants yet, so i'm guessing it can be solved without using it.
nevertheless, from what i read in wiki, if matrix A is invetrtible, then its determinant is not 0.
and since i want to prove the contrapositive, i need to assume it's singular, and the its det is equal 0.
so:
i can multiply it by det(A) times, and then say that
but what conclusion can i draw from it?
does that prove it?
BTW, i have no idea what determinant is, so bare with me...