If $A^2 = - I$, is $A$ invertible?
My attempt: We know $A^4 = I$. So, $A(A^3) = I$, and thus, the inverse of $A$ is $A^3$. Is that correct?
It is a really basic question but it's a new subject for me.
2026-04-01 03:41:24.1775014884
If $A^2 = - I$, is $A$ invertible?
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$A(-A) = (-A)A = I$. So the inverse of $A$ is ... .