Hello, I have problem with matrices. Can somebody help me, Please....(Crying)

If P^2 = P and P^-1 exists, find the determinant P and show that (I+P)^2 = I + 7P

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- September 17th 2012, 08:22 PMAuXianHelp me...
Hello, I have problem with matrices. Can somebody help me, Please....(Crying)

If P^2 = P and P^-1 exists, find the determinant P and show that (I+P)^2 = I + 7P - September 18th 2012, 12:06 AMchiroRe: Help me...
Hey AuXian.

Firstly, if you have square matrices A and B then det(AB) = det(A)det(B) and P has to be square so if P^2 = P then det(P^2) = det(P)det(P) = det(P) which means that det(P) = 1 or 0. But if P has an inverse it can't equal 0 so it has to be 1.

Now for the second example, what is your distributive rule when it comes to matrices (i.e what is (A+B)^2 if it equals (A+B)(A+B))?