Recent content by craigy

Thanks radou, after some thought, I figured out that 1 and 3 are the only formulas that hold for all invertible n x n matrices A and B.

I sub n is an identity matrix. 2, 3 and 5 seems to work when using a diagonal matrix.

I know that but that doesn't solve the problem

1. Homework Statement Determine which of the formulas hold for all invertible nxn matrices A and B 1. (In-A)(In+A) = In - A^2 2. (A+B)(A-B) = A^2 - B^2 3. A^8*B^5 is invertible 4. (A+A^-1)^9 = A^9 + A^-9 5. AB = BA 6. A+A^-1 is invertible I know 5 is right, and number 2 wrong...