Question
The number of distinct real roots
of $$\left| {\matrix{ {\sin x} & {\cos x} & {\cos x} \cr {\cos x} & {\sin x} & {\cos x} \cr {\cos x} & {\cos x} & {\sin x} \cr } } \right| = 0$ in the interval $ - {\pi \over 4} \le x \le {\pi \over 4}$$ is :
of $$\left| {\matrix{ {\sin x} & {\cos x} & {\cos x} \cr {\cos x} & {\sin x} & {\cos x} \cr {\cos x} & {\cos x} & {\sin x} \cr } } \right| = 0$ in the interval $ - {\pi \over 4} \le x \le {\pi \over 4}$$ is :