Question

If A is a square matrix such that $A^2=I$, then $A^{-1}$ is equal to

• A. I
• B. O
• C. A
• D. A + I

Answer 1

Answer: (C)

$A^2=I\Rightarrow AA=I\Rightarrow A^{-1}\left(AA\right)=A^{-1}I$
$\Rightarrow A=A^{-1}$