Simplify $\sin (x - y) \cos y + \cos (x - y) \sin y.$
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Simplify $\sin (x - y) \cos y + \cos (x - y) \sin y.$
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
\sin x
Simplify $\sin (x - y) \cos y + \cos (x - y) \sin y.$
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