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转贴:试用sinθ表示sin3θ

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1楼2012-10-05 11:42回复
    sin3θ
    =sin(2θ+θ)
    =sin2θcosθ+cos2θsinθ
    =2sinθcosθcosθ+(1-2(sinθ)^2)sinθ
    =2sinθ(1-(sinθ)^2)+(1-2(sinθ)^2)sinθ
    =2sinθ-2(sinθ)^3+sinθ-2(sinθ)^3
    =3sinθ-4(sinθ)^3


    本楼含有高级字体2楼2012-10-05 11:42
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