Since [tex]A^2=A[/tex], we have
[tex](I + A)^2 = I^2 + IA + AI + A^2 = I + A + A + A = I + 3A[/tex]
[tex](I + A)^3 = (I + A) (I + 3A) = I^2 + 3IA + AI + 3A^2 = I + 3A + A + 3A = I + 7A[/tex]
Then the target expression is
[tex]7A - (I + A)^3 = 7A - (I + 7A) = \boxed{-I}[/tex]
