SOLUTION: Use a sum or difference formula to find the exact value of the following. cos 2(pi)/5 cos(pi)/15 + sin2(pi)/5 sin(pi)/15

Question 1060407: Use a sum or difference formula to find the exact value of the following.
cos 2(pi)/5 cos(pi)/15 + sin2(pi)/5 sin(pi)/15
Answer by ikleyn(52786) (Show Source): You can put this solution on YOUR website!
.

 =  =  =  =  = .


The sum or difference formulas for cosine are

cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b),

cos(a-b) = cos(a)*cos(b) + sin(a)*sin(b).

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