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## Homework Statement

Determine which of the formulas hold for all invertible nxn matrices A and B

1. (A+A^-1)^7 = A^7+A^-7

2. 2A is invertible

3. (A+B)² = A² + B² + 2AB

4. (ABA^-1)^6 = AB^6A^-1

5. A + B is invertible

6. ABA^-1 = B

I know 2A should be invertible, and number 3 wrong, but what else?

Thanks