Answer
See answer below
Work Step by Step
$A, B, C$ are $n \times n$ matrices satisfying $B A = I_n$ and $AC = I_n$
Multiplying both sides of $B A = I_n$ by $C$:
$(B A)C = I_nC$
We have $(B A)C = B(AC)=BI_n=B$
and $I_nC=C$
Then $B=C$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.