Question

Need help with this problem. ​

Answer 1

C)
`-(47)/(49)`

Explanation:

By the cos double angle formula, we know
`\cos(2\theta)=2\cos^2\theta-1.` Substituting
`\cos \theta` into the formula, we get

`\cos(2\theta)=2(-(1)/(7))^2-1\\~~~~~~~~~~=(2)/(49)-1\\~~~~~~~~~~=\boxed{-(47)/(49)}`.

The answer is C.