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

$(a)\;A+I\qquad(b)\;A\qquad(c)\;0\qquad(d)\;2A$

$A^2=I$
$\Rightarrow A^2A^{-1}=IA^{-1}$
$\Rightarrow A=A^{-1}$
Hence (b) is the correct answer.