Mathematics | VITEEE 2014 | Discussion Page

1)

If $A=\begin{bmatrix}3 & 4 \\5 & 7 \end{bmatrix}$ , then A , (adj A) is equal to

A) A

B) |A|

C) |A|

D) none of these

Option C

$A=\begin{bmatrix}3 & 4 \\5 & 7 \end{bmatrix}$

|A|=21-20=1

$\therefore$ $A(adj A)=\begin{bmatrix}3 & 4 \\5 & 7 \end{bmatrix}\begin{bmatrix}7 & -4 \\-5 & 3 \end{bmatrix}$

= $\begin{bmatrix}1 & 0 \\0 & 1 \end{bmatrix}=1.\begin{bmatrix}1 & 0 \\0 & 1 \end{bmatrix}=|A|.1$

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