Let A and B be n×n matrices. If AB is invertible, show that both A and B are invertible

Linear Algebra: A Modern Introduction
4th Edition
ISBN:9781285463247
Author:David Poole
Publisher:David Poole
Chapter2: Systems Of Linear Equations
Section2.2: Direct Methods For Solving Linear Systems
Problem 60EQ
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Let A and B be n×n matrices. If AB is invertible, show that both A and B are invertible using Theorem 2.4.5

Theorem 2.4.5: Inverse Theorem
The following conditions are equivalent for an n×n matrix A:
1. A is invertible.
2. The homogeneous system Ax = 0 has only the trivial solution x = 0.
3. A can be carried to the identity matrix In by elementary row operations.
4. The system Ax = b has at least one solution x for every choice of column b.
5. There exists an n×n matrix C such that AC = In.

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