March 19th, 2010
  • These are the only questions I don't understand and don't know the answer, thank you for helping.

    Determine which of the formulas hold for all invertible nxn matrices A and B
    A. AB=BA
    B. A^5 is invertible
    C. (A+B)(A−B)=A^2−B^2
    D. (AB)^−1=A^−1B^−1
    E. A+B is invertible
    F. (In−A)(In+A)=In−A^2

    If (A - B)(A + C) = I, where I is the 66 identity matrix, and A, B and C are ANY matrices, find ALL correct statements)

    A. (A - B) is invertible
    B. A and B are the same size and invertible
    C. (A + C) is invertible
    D. A and C are the same size
    E. None of the above

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

    A. A+B is invertible
    B. ABA^−1=B
    C. (A+A^−1)^7=A^7+A^−7
    D. A^2B^5 is invertible
    E. (In+A)(In+A^−1)=2In+A+A^−1
    F. (A+B)^2=A^2+B^2+2AB


  • For the first set of formulas I don't know what (In-A)(In+A) means.

    Other than that, I think that only B holds.

    I am not sure about the other sets of formulas.







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