Answer:
Explanation:
Given:
[tex]\cos x\text{ =}\frac{\sqrt[]{15}}{4}[/tex]
We must remember that:
[tex]\cos (2x)=2\cos ^2x-1[/tex]
Since the value of cos x is given, we plug in the value into 2cos^2x-1. So,
[tex]\begin{gathered} 2\cos ^2x-1 \\ =2(\frac{\sqrt[]{15}}{4})^2-1 \\ \text{Simplify} \\ =2(\frac{15}{16})-1 \\ \text{Calculate} \\ =\frac{7}{8} \end{gathered}[/tex]
Therefore, the exact value of cos 2x is 7/8.
