 #1
 23
 1
 Homework Statement:

\begin{array}{l}
\tan 2 \theta=\frac{4}{3} \\
\text {Find } \\
\text { a) } \cos \theta \\
\text { b) } \sin \theta
\end{array}
 Relevant Equations:
 N/A. Answer is needed as a fraction.
So I get that:
$$
\sin 2 \theta=\frac{4}{5}
$$
$$
\cos 2 \theta=\frac{3}{5}
$$
But what is the next step?
$$
\sin 2 \theta=\frac{4}{5}
$$
$$
\cos 2 \theta=\frac{3}{5}
$$
But what is the next step?
We find that ##\cos 2 \theta=3 / 5,## the minus entering because ##2 \theta## is a second quadrant angle. Then ##\sin \theta=2 / \sqrt{5}## and ##\cos \theta=1 / \sqrt{5} .##