Evaluate the following using double angle concepts

1.Cos^15 - sin^15

2. 2sin15 cos15
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I think you mean cos^2(15)-sin^2(15)=cos(2*15)=cos(30)=sqrt(3)/2=0.8660 approx.

The second one is sin(2*15)=sin(30)=0.5 exactly.
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