Question
Show each step to show how to verify the identity.
cos(x + y) + cos(x - y) = 2 cos x cos y
cos(x + y) + cos(x - y) = 2 cos x cos y
Answers
use your sum/difference formulas:
cos(x+y) = cosx cosy - sinx siny
now use the difference formula, and then add them up and see what drops out.
cos(x+y) = cosx cosy - sinx siny
now use the difference formula, and then add them up and see what drops out.
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