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## Main Question or Discussion Point

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

A. AB=BA

B. (A+A^–1)^8=A^8+A^–8

C. A^5 is invertible

D. A+A^–1 is invertible

E. (In+A)(In+A^–1)=2In+A+A^–1 (where In is the identity matrix)

F. (A+B)^2=A^2+B^2+2AB

I was able to find counterexamples to prove A and B and F incorrect. However, the webwork program (designed for practicing basic Linear Algebra) I am using states that C, D, and E are not all correct ... what am I missing?

A. AB=BA

B. (A+A^–1)^8=A^8+A^–8

C. A^5 is invertible

D. A+A^–1 is invertible

E. (In+A)(In+A^–1)=2In+A+A^–1 (where In is the identity matrix)

F. (A+B)^2=A^2+B^2+2AB

I was able to find counterexamples to prove A and B and F incorrect. However, the webwork program (designed for practicing basic Linear Algebra) I am using states that C, D, and E are not all correct ... what am I missing?

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