જો $A = \left[ {\begin{array}{*{20}{c}}{\cos \alpha }&{\sin \alpha }\\{ - \sin \alpha }&{\cos \alpha }\end{array}} \right]$ અને $A\,\,\text{adj } A = \left[ {\begin{array}{*{20}{c}}k&0\\0&k\end{array}} \right],$ તો $ k=$
A$0$
B$1$
C$\sin \alpha \cos \alpha $
D$\cos 2\alpha $
Medium
Download our app for free and get started
B$1$
Let $A = \left[ {\begin{array}{*{20}{c}}{\cos \alpha }&{\sin \alpha }\\{ - \sin \alpha }&{\cos \alpha }\end{array}} \right]$ The matrix of cofactors of the elements of $A,$
$A = \left[ {\begin{array}{*{20}{c}}{\cos \alpha }&{-(-\sin \alpha) }\\{ - \sin \alpha }&{\cos \alpha }\end{array}} \right]$
$\therefore \text{adj}\ A = $the transpose of matrix of cofactors of $ A$
$A = \left[ {\begin{array}{*{20}{c}}{\cos \alpha }&{-\sin \alpha }\\{ - \sin \alpha }&{\cos \alpha }\end{array}} \right]$
$\therefore A\ \text{adj} \ A = \left[ {\begin{array}{*{20}{c}}{\cos \alpha }&{\sin \alpha }\\{ - \sin \alpha }&{\cos \alpha }\end{array}} \right]\,\,\left[ {\begin{array}{*{20}{c}}{\cos \alpha }&{ - \sin \alpha }\\{\sin \alpha }&{\cos \alpha }\end{array}} \right]$
$= \left[ {\begin{array}{*{20}{c}}1&0\\0&1\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}k&0\\0&k\end{array}} \right] \ ($as given$)$
$ \Rightarrow K=1.$
Download our app
and get started for free
Experience the future of education. Simply download our apps or reach out to us for more information. Let's shape the future of learning together!No signup needed.*
ધારો ક $A.P$. (સમાંતર શ્રેણી) ના ત્રણ ભિત્ર ક્રમિક પદો $a, b, c$ માટે રેખાઓ$a x+b y+c=0$ બિંદુ $\mathrm{P}$ પર સંગામી થાય છે તથા $\mathrm{Q}(\alpha, \beta)$ એવું બિંદુ છે કે જેથી સમીકરણ સંહતિ $x+y+z=6 \text {, }$ , $2 x+5 y+\alpha z=\beta $ અને $x+2 y+3 z=4 $ ને અનંત ઉકેલો મળે. તો $(\mathrm{PQ})^2=. . . . . $