If $A=\begin{bmatrix}-1 & 1 & 4\\1 & 5 & 7\\4 & 7 & 8\end{bmatrix}$, is then 2A + 7A′ is equal to:
Answer & explanation
Correct answer: option 2
$2A+7A'=\begin{bmatrix}-2 & 2 & 8\\2 & 10 & 14\\8 & 14 & 16\end{bmatrix}+\begin{bmatrix}-7 & 7 & 28\\7 & 35 & 49\\28 & 49 & 56\end{bmatrix}=9A$
∵ A' = A
∴ 2A + 7A' = 2A + 7A = 9A