<|system|>
Compute $\arccos \left (-\frac{1}{\sqrt{2}} \right).$  Express your answer in radians.</s>.
<|user|>
Can you answer based on context?
<|assistant|>
Since $\cos \frac{3 \pi}{4} = -\frac{1}{\sqrt{2}},$ $\arccos \left( -\frac{1}{\sqrt{2}} \right) = \frac{3 \pi}{4}.$