Question

Need help with this problem. ​

Answer 1

Answer:

C) $-\frac{47}{49}$

Step-by-step 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

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

The answer is C.