3 and 4 .Determinants and Matrices
easy

यदि $A = \left[ {\begin{array}{*{20}{c}}{\,\,\,\cos \alpha }&{\sin \alpha }\\{ - \sin \alpha }&{\cos \alpha }\end{array}} \right]$, तो ${A^2} = $

A

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

B

$\left[ {\begin{array}{*{20}{c}}{\cos 2\alpha }&{ - \sin 2\alpha }\\{\sin 2\alpha }&{\cos 2\alpha }\end{array}} \right]$

C

$\left[ {\begin{array}{*{20}{c}}{\,\,\,\cos 2\alpha }&{\sin 2\alpha }\\{ - \sin 2\alpha }&{\cos 2\alpha }\end{array}} \right]$

D

$\left[ {\begin{array}{*{20}{c}}{ - \cos 2\alpha }&{\sin 2\alpha }\\{ - \sin 2\alpha }&{ - \cos 2\alpha }\end{array}} \right]$

Solution

(c) ${A^2} = A\,.\,A = \left[ {\begin{array}{*{20}{c}}{\cos \alpha }&{\sin \alpha }\\{ – \sin \alpha }&{\cos \alpha }\end{array}} \right]\,\,\left[ {\begin{array}{*{20}{c}}{\cos \alpha }&{\sin \alpha }\\{ – \sin \alpha }&{\cos \alpha }\end{array}} \right]$ = $\left[ {\begin{array}{*{20}{c}}{\cos 2\alpha }&{\sin 2\alpha }\\{ – \sin 2\alpha }&{\cos 2\alpha }\end{array}} \right]$.

Standard 12
Mathematics

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