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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