If $\cos \theta = \frac{2}{3},$ then find $\cos 2 \theta.$
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If $\cos \theta = \frac{2}{3},$ then find $\cos 2 \theta.$
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
-\frac{1}{9}
If $\cos \theta = \frac{2}{3},$ then find $\cos 2 \theta.$
train