3 and 4 .Determinants and Matrices
easy

જો $A = \left( {\begin{array}{*{20}{c}}1&2&3\\3&1&2\\2&3&1\end{array}} \right)$ અને $B = \left( {\begin{array}{*{20}{c}}{ - 5}&7&1\\1&{ - 5}&7\\7&1&{ - 5}\end{array}} \right)$ તો $AB$ = . . .

A

${I_3}$

B

$2{I_3}$

C

$4{I_3}$

D

$18{I_3}$

Solution

(d) We have $A = \left[ {\begin{array}{*{20}{c}}1&2&3\\3&1&2\\2&3&1\end{array}} \right]$ and $B = \left[ {\begin{array}{*{20}{c}}{ – 5}&7&1\\1&{ – 5}&7\\7&1&{ – 5}\end{array}} \right]$

$\therefore $ $AB = \left[ {\begin{array}{*{20}{c}}1&2&3\\3&1&2\\2&3&1\end{array}} \right]\,\,\left[ {\begin{array}{*{20}{c}}{ – 5}&7&1\\1&{ – 5}&7\\7&1&{ – 5}\end{array}} \right]$

$AB = \left[ {\begin{array}{*{20}{c}}{18}&0&0\\0&{18}&0\\0&0&{18}\end{array}} \right] = 18\,\left[ {\begin{array}{*{20}{c}}1&0&0\\0&1&0\\0&0&1\end{array}} \right]$

$AB = 18\,{I_3}$.

Standard 12
Mathematics

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