The number of solutions of $12 {cos}^{3} x - 7 {cos}^{2} x + 4 cos x = 9$ is

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Infinite

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None of these

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Solution

The correct option is B Infinite
Given, $12 {cos}^{3} x - 7 {cos}^{2} x + 4 cos x - 9 = 0$
$cos x = 1$ (only real solution)
$x = 2 n π \pm \frac{π}{2}$
So, it has infinite solutions.

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