Question 1084680: cos(60°+A)+cos(60°-A)-cosA=0
Answer by htmentor(1343)   (Show Source):
You can put this solution on YOUR website! I assume the problem involves proving the identity. If so, we proceed as follows:
Using trig identities, we can write cos(60°+A)+cos(60°-A)-cosA as
cos(60)cos(A) - sin(60)sin(A) + cos(60)cos(A) + sin(60)sin(A) - cos(A)
The sine terms cancel, and we are left with
2cos(60)cos(A) - cos(A) -> cos(A)(2cos(60) - 1)
Since cos(60) = 1/2, 2cos(60) - 1 = 0, and thus the original expression equals zero for all values of A.
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