3 and 4 .Determinants and Matrices
easy

If $A + B = \left[ {\begin{array}{*{20}{c}}1&0\\1&1\end{array}} \right]$and $A - 2B = \left[ {\begin{array}{*{20}{c}}{ - 1}&1\\0&{ - 1}\end{array}} \right]\,,$ then $A=$

A

$\left[ {\begin{array}{*{20}{c}}1&1\\2&1\end{array}} \right]$

B

$\left[ {\begin{array}{*{20}{c}}{2/3}&{1/3}\\{1/3}&{2/3}\end{array}} \right]$

C

$\left[ {\begin{array}{*{20}{c}}{1/3}&{1/3}\\{2/3}&{1/3}\end{array}} \right]$

D

None of these

Solution

(c) $2A + 2B = \left[ {\begin{array}{*{20}{c}}2&0\\2&2\end{array}} \right]$, $A – 2B = \left[ {\begin{array}{*{20}{c}}{ – 1}&1\\0&{ – 1}\end{array}} \right]$

On adding, we get$3A = \left[ {\begin{array}{*{20}{c}}1&1\\2&1\end{array}} \right]$

$ \Rightarrow \,A = \left[ {\begin{array}{*{20}{c}}{1/3}&{1/3}\\{2/3}&{1/3}\end{array}} \right]$.

Standard 12
Mathematics

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