1. 設cos4x=1/4,求(1)cos^4x-sin^4x (cos^2 x + sin^2 x) (cos^2 x - sin^2 x) =1 (cos^2 x - sin^2 x)=cos 2x cos^2 2x =(cos4x + 1)/2=(1/4 + 1)/2=5/8 cos ...
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