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Q. If $A^2 - A + I = 0$ , then the inverse of A is

Determinants

Solution:

Given $A^2 - A + I = 0$
$A^{-1} A^2 - A^{-1} A + A^{-1}.I = A^{-1}.0$
(Multiplying $A^{-1}$ on both sides)
$\Rightarrow \, A -1+ A^{-1} = 0$ or $A^{-1} = I - A$.