3 and 4 .Determinants and Matrices
easy

If $3X + 2Y = I$ and $2X - Y = O$, where $ I$  and $ O $ are unit and null matrices of order $3 $ respectively, then

A

$X = (1/7),Y = (2/7)$

B

$X = (2/7),Y = (1/7)$

C

$X = (1/7)I,Y = (2/7)\,I$

D

$X = (2/7)\,I,Y = (1/7)\,I$

Solution

(c) $\begin{array}{l}3X + 2Y = I\\2X – Y = O\end{array}$ $ \Rightarrow $ $\begin{array}{l}3X + 2Y = I\\4X – 2Y = O\end{array}$ $ \Rightarrow $ $\begin{array}{l}7X = I\\\,\,X = \frac{1}{7}I\end{array}$

                                                                                                  (Solving simultaneously)

Therefore from $(i),$ $2Y = I – \frac{3}{7}I = \frac{4}{7}I \Rightarrow Y = \frac{2}{7}I$.

Standard 12
Mathematics

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