cos(θ+2θ)=cosθcos2θ-sinθsin2θ
=cosθ(cos^2 θ-sin^2 θ)-2cosθsin^2 θ
=cos^3 θ-3cosθ(1-cos^2 θ)
=4cos^3 θ-3cosθ
Mathematics
Senior High
なぜこうなるのか証明できるかたいませんか？
a Use complex number methods to de UC(
lcos30 三 4cos9の8 Co8
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