If $0 \le x < 2\pi $ , then the number of real values of $x,$ which satisfy the equation $\cos x + \cos 2x + \cos 3x + \cos 4x = 0$ is . . .
$7$
$9$
$3$
$5$
Let $f(x) = \cos \sqrt {x,} $ then which of the following is true
The number of values of $x$ in the interval $[0, 5\pi]$ satisfying the equation $3sin^2x\, \,-\,\, 7sinx + 2 = 0$ is
If $\cos A\sin \left( {A - \frac{\pi }{6}} \right)$ is maximum, then the value of $A$ is equal to
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The equation $3{\sin ^2}x + 10\cos x - 6 = 0$ is satisfied, if