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3 and 4 .Determinants and Matrices
easy
Evaluate the determinants : $\left|\begin{array}{ll}\cos \theta & -\sin \theta \\ \sin \theta & \cos \theta\end{array}\right|$
A
$0$
B
$-1$
C
$1$
D
$2$
Solution
$\left| {\begin{array}{*{20}{c}}
{\cos \theta }&{ – \sin \theta } \\
{\sin \theta }&{\cos \theta }
\end{array}} \right|$
$ = (\cos \theta )(\cos \theta ) – ( – \sin \theta )(\sin \theta )$
$ = {\cos ^2}\theta + {\sin ^2}\theta $
$ = 1$
Standard 12
Mathematics