SOLUTION: verify the question algebraically cos(x-y)+cos(x+y)=2cosxcosy

Question 596221: verify the question algebraically
cos(x-y)+cos(x+y)=2cosxcosy
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
cos(x-y)+cos(x+y)=2cos(x)cos(y)

[cos(x)cos(y)+sin(x)sin(y)]+[cos(x)cos(y)-sin(x)sin(y)]=2cos(x)cos(y)

cos(x)cos(y)+sin(x)sin(y)+cos(x)cos(y)-sin(x)sin(y)=2cos(x)cos(y)

[cos(x)cos(y)+cos(x)cos(y)]+[sin(x)sin(y)-sin(x)sin(y)]=2cos(x)cos(y)

2cos(x)cos(y)=2cos(x)cos(y)

This verifies the identity.
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