Show that if a square matrix A satisfies $A^2 - 3A + I = 0$ then $A^-1 = 3I - A$
2. Given is: $A^2-3A+I = 0 \Longrightarrow I = -A^2+ 3A$
Now observe that $A(3I-A) = -A^2+3A = I$. Hence $A^{-1} = 3I-A$