Question

Please help me figure out this problem i don’t know if i did it right

Answer 1

Step-by-step explanation:

Given:

`\cos x\text{ =}\frac{\sqrt[]{15}}{4}`

We must remember that:

`\cos (2x)=2\cos ^2x-1`

Since the value of cos x is given, we plug in the value into 2cos^2x-1. So,

`\begin{gathered} 2\cos ^2x-1 \\ =2(\frac{\sqrt[]{15}}{4})^2-1 \\ \text{Simplify} \\ =2((15)/(16))-1 \\ \text{Calculate} \\ =(7)/(8) \end{gathered}`

Therefore, the exact value of cos 2x is 7/8.