Question

Can someone help me find cos 2theta if sin (theta)=1/7? I think I would use the identity 1-sin^2 theta to replace cos2theta, but I'm not sure.

Answer 1

\(\Large \cos^2\theta \qquad\text{or}\qquad \cos(2\theta)\)
?

Answer 2

Cos (2theta)

Answer 3

\[\cos(2\theta)=\cos^2\theta-\sin^2\theta=1-2\sin^2\theta\Rightarrow\]
\[\Rightarrow \cos(2\theta)=1-2(1/7)^2=47/49\]

Answer 4

Thank you