140- If $A = \begin{bmatrix} 1 & -1 & 2 \\ 0 & 2 & -1 \\ 0 & 0 & 3 \end{bmatrix}$, what is the sum of the entries of the second column of $A^{-1}$? (1) $-\dfrac{1}{3}$ (2) $\dfrac{2}{3}$ (3) $1$ (4) zero
\textbf{140-} If $A = \begin{bmatrix} 1 & -1 & 2 \\ 0 & 2 & -1 \\ 0 & 0 & 3 \end{bmatrix}$, what is the sum of the entries of the second column of $A^{-1}$?
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(1) $-\dfrac{1}{3}$ \hfill (2) $\dfrac{2}{3}$
(3) $1$ \hfill (4) zero
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