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Sum Identities

QuestionAnswer
sinx + cosu 2sin((x + y)/2)cos((x - y)/2)
sinx - siny 2cos((x + y)/2)sin((x - y)/2)
cosx + cosy 2cos((x + y)/2)cos((x - y)/2)
cosx - cosy -2sin((x + y)/2)sin((x - y)/2)
Created by: kalensnyder
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