If $A=\begin{bmatrix}-1 & 1 & 4\

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Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Matrices

Question:

If $A=\begin{bmatrix}-1 & 1 & 4\\1 & 5 & 7\\4 & 7 & 8\end{bmatrix}$, is then 2A + 7A′ is equal to:

Options:

12A

17A

Correct Answer:

Explanation:

$2A+7A'=\begin{bmatrix}-2 & 2 & 8\\2 & 10 & 14\\8 & 14 & 16\end{bmatrix}+\begin{bmatrix}-7 & 7 & 28\\7 & 35 & 49\\28 & 49 & 56\end{bmatrix}=9A$

∵ A' = A

∴ 2A + 7A' = 2A + 7A = 9A