SOLUTION: Express as a product cosa+2cos7a+cos13a I know formulas but not how to apply

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Question 1126039: Express as a product
cosa+2cos7a+cos13a
I know formulas but not how to apply
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Express as a product
cosa+2cos7a+cos13a = (1/4)*(4cosa + 8cos7a + 4cos13a)