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3 and 4 .Determinants and Matrices
easy
જો $A = \left( {\begin{array}{*{20}{c}}2&{ - 1}\\{ - 1}&2\end{array}} \right)$ અને $I$ એ 2 કક્ષા વાળો એકમ શ્રેણિક હોય તો ${A^2}$ = . . .
A
$4A - 3I$
B
$3A - AI$
C
$A - I$
D
$A + I$
Solution
(a)${A^2} = A\,.\,A = \left[ {\begin{array}{*{20}{c}}{\rm{2}}&{ – 1}\\{ – 1}&2\end{array}} \right]\,\left[ {\begin{array}{*{20}{c}}{\rm{2}}&{ – 1}\\{ – 1}&2\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}{\rm{5}}&{ – 4}\\{ – 4}&5\end{array}} \right]$
==> $4A – 3I = \,\left[ {\begin{array}{*{20}{c}}{\rm{8}}&{ – 4}\\{ – 4}&8\end{array}} \right]\, – \,\left[ {\begin{array}{*{20}{c}}{\rm{3}}&0\\0&3\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}5&{ – 4}\\{ – 4}&5\end{array}} \right]$.
Standard 12
Mathematics