MCQ
If $A^5 = 0$ Such that $\text{A}^{\text{n}}\neq\text{I}$ for $1\leq\text{n}\leq4,$ then $(\text{I}-\text{A})^{-1}$ equals :
  • A
    $A^4$
  • B
    $A^3$
  • C
    $I + A$
  • None of these.

Answer

Correct option: D.
None of these.
$A^5=0$
Using $a^5-b^5=(a-b)\left(a^4+a^3 b+a^2 b^2+a b^3+b^4\right)$
$I-A^5=(I-A)\left(I+A+A^2+A^3+A^4\right)$
$I=(I-A)\left(I+A+A^2+A^3+A^4\right)$
$(I-A)^{-1} I=(I-A)^{-1}(I-A)\left(I+A+A^2+A^3+A^4\right)$
$(I-A)-1=I+A+A^2+A^3+A^4$

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