Question

If $4{\cos }^{2}x=3$ and x is an acute angle; find the value of $\cos 3x$

• A. $0$
• B. $\sqrt{3}$
• C. $\sqrt{2}$
• D. $\frac{1}{2}$

Answer 1

The correct option is A $0$

$4{\cos }^{2}x=3$
${\cos }^{2}x=\frac{3}{4}$
$\cos x=\frac{\sqrt{3}}{2}$
$\cos x=\cos 30$
$x={30}^{\circ }$
Now, $\cos 3x=\cos {90}^{\circ }=0$