Evaluate the Expression $\sin x \sin ( x + y ) + \cos x \cos ( x + y )$

question 19

Multiple Choice

Evaluate the expression.​ $\sin x \sin ( x + y ) + \cos x \cos ( x + y )$ ​

• A) \(\sin ^ { 2 } x - \sin ^ { 2 } y\)
• B)0
• C) \(\sin x \cos x + \sin y \cos y\)
• D) \(\cos y\)
• E) \(\cos ^ { 2 } x - \sin ^ { 2 } x\)

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