Question
A, B, C are three non-null square matrices of the same order, write the condition on A such that AB = AC ⇒ B = C.

Answer

Consider AB = AC.

On multiplying both sides by A-1, we get

AA-1B = AA-1

⇒ IB = IC [Because AA-1 = I where I is the identity matrix]

⇒ B = C 

Therefore, the required condition is A must be invertible or $|\text{A}|\neq0$.

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