\frac{3 \pi}{4}
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Compute $\arccos \left (-\frac{1}{\sqrt{2}} \right).$  Express your answer in radians.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
\frac{3 \pi}{4}
Compute $\arccos \left (-\frac{1}{\sqrt{2}} \right).$  Express your answer in radians.
train