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Question: Answered & Verified by Expert
Let $\mathrm{A}$ and $\mathrm{B}$ be any two $\mathrm{n} \times \mathrm{n}$ matrices such that the following conditions hold : $\mathrm{AB}=\mathrm{BA}$ and there exist positive integers $\mathrm{k}$ and $\ell$ such that $\mathrm{A}^{\mathrm{k}}=\mathrm{I}$ (the identity matrix) and $\mathrm{B}^{\prime}=0$ (the zero matrix). Then-
MathematicsDeterminantsKVPYKVPY 2011 (SB/SX)
Options:
  • A $\mathrm{A}+\mathrm{B}=\mathrm{I}$
  • B $\operatorname{det}(\mathrm{AB})=0$
  • C $\operatorname{det}(\mathrm{A}+\mathrm{B}) \neq 0$
  • D $(\mathrm{A}+\mathrm{B})^{\mathrm{m}}=0$ for some integer $\mathrm{m}$
Solution:
2805 Upvotes Verified Answer
The correct answer is: $\operatorname{det}(\mathrm{AB})=0$
$A^{k}=I, B^{\ell}=0($ det $(B)=0)$
$\Rightarrow \operatorname{det}(A B)=0$

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