Do Homework - Brandon Frey- MyMathLab Pearson https://www.mathd.com/Student/Play
ID: 3018263 • Letter: D
Question
Explanation / Answer
We know that
cos A + cos B = 2*cos(A+B)/2*cos(A-B)/2
Then
cos3 + cos9 = 2*cos(3 + 9)/2*cos(3 - 9)/2 = 2*cos6*cos(-3) = 2*cos6*cos(3)
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