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4.4.3. Suppose A and B are n × n matrices. Prove that, if AB is invertible,...

4.4.3. Suppose A and B are n × n matrices. Prove that, if AB is invertible, then A and B are both invertible. Do not use determinants, since we have not seen them yet. Hint: Use Lemma 4.4.4.

Lemma 4.4.4. If A ∈ Mm,n(F) and B ∈ Mn,k(F), then rank(AB) ≤ rank(A) and rank(AB) ≤ rank(B).

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