If \sum_{n=0}^{\infty} \cos ^{2 n} \theta=5, what is the value of \cos 2 \theta ?
Answer Choices
A. \dfrac{1}{5}
B. \dfrac{2}{5}
C. \dfrac{\sqrt{5}}{5}
D. \dfrac{3}{5}
E. \dfrac{4}{5}
If \sum_{n=0}^{\infty} \cos ^{2 n} \theta=5, what is the value of \cos 2 \theta ?
Answer Choices
A. \dfrac{1}{5}
B. \dfrac{2}{5}
C. \dfrac{\sqrt{5}}{5}
D. \dfrac{3}{5}
E. \dfrac{4}{5}