$D=\left|\begin{array}{ccc}3 \sin 3 \theta & -1 & 1 \\3 \cos 2 \theta & 4 & 3 \\6 & 7 & 7\end{array}\right|=0$$21 \sin 3 \theta+42 \cos 2 \theta-42=0$$\sin 3 \theta+2 \cos 2 \theta-2=0$
Number of solution is $7$ in $(0,4 \pi)$
વિધાન $ 1: $ જો $A \ne I,A \ne - I$ તો $\det \left( A \right) = - 1$
વિધાન $2:$ જો $A \ne I,A \ne - I$ તો ${\rm{tr}}\left( A \right) \ne 0$