Matrices & Determinants
Properties of matrices with MN=M, NM=N
MMTS_Full_Test_02
Grade 12

Question:

Let $M$ and $N$ be square matrices of the same order satisfying $MN = M$ and $NM = N$. Then $(M^{2024} + N^{2024})^{2025}$ is equal to
(A) $M + N$
(B) $2025(M+N)$
(C) $2^{2024}(M+N)$
(D) $2^{2025}(M+N)$

Step-by-Step Solution

Key Concept: Derive $M^2 = M$ and $N^2 = N$ (both are idempotent). Then compute powers of $M$ and $N$, and use the binomial theorem on the sum.
$M^2=M$, $N^2=N$, $MN+NM=M+N$. $(M+N)^2=2(M+N) \Rightarrow (M+N)^{2025}=2^{2024}(M+N)$. Also $M^{2024}=M$, $N^{2024}=N$.
Correct Answer: (C) $2^{2024}(M+N)$

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