Compute $\cos 180^\circ$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Compute $\cos 180^\circ$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
-1
Compute $\cos 180^\circ$.
train