SOLUTION: Prove that cos35 + cos45 + cos75 + cos85 = 2cos5cos20

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Question 1137787: Prove that cos35 + cos45 + cos75 + cos85 = 2cos5cos20
Found 2 solutions by MathLover1, Alan3354:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

prove that
cos%2835%29+%2B+cos%2845+%29%2B+cos%2875%29+%2B+cos%2885%29+=+2cos%285%29cos%2820+%29



=> statement is FALSE (the two sides are not equal)

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Using a calculator, they are equal.
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I don't plan to do any more on this one.