Question

If $\left|\begin{array}{ccc}\cos \theta & -1& 1\\ \cos 2\theta & 4& 3\\ 2& 7& 7\end{array}\right|=0$ then the number of values of $\theta$ in $[0,2\pi ]$

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (B)

$\cos \theta =\frac{-1\pm \sqrt{65}}{8}$
Hence number of solutions $=2$