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3 and 4 .Determinants and Matrices
hard
$\theta \in (0,\pi)$ ની કેટલી કિમંત માટે રેખીય સમીકરણો $x + 3y + 7z = 0$ ; $-x + 4y + 7z = 0$ ; $ (sin\,3\theta )x + (cos\,2\theta )y + 2z = 0$ ને શૂન્યતર ઉકેલ ધરાવે .
A
$3$
B
$2$
C
$4$
D
$1$
(JEE MAIN-2019)
Solution
$\left| {\begin{array}{*{20}{c}}
{\sin 3\theta }&{ – 1}&1\\
{\cos 2\theta }&4&3\\
2&7&7
\end{array}} \right| = 0$
$7\sin 3\theta + 14\cos 2\theta – 14 = 0$
$\sin 3\theta + 2\cos 2\theta – 2 = 0,\sin \theta = \frac{1}{2}$
Standard 12
Mathematics
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