tanα=a,求(3sinα+sin3α)/(3c - 知识问答

tanα=a,求(3sinα+sin3α)/(3cosα+cos3α)的值

1个回答

（3sina+sin3a)/(3cosa+cos3a)
=(3sina+3sina-4sin^3a)/(3cosa+4cos^3a-3cosa)
=(6sina-4sin^3a)/(4cos^3a)
=3/2tana*1/cos^2a-tan^3a
=3/2a*(1+tan^2a)-a^3
=3/2a+3/2a^3-a^3
=3/2a+a^3/2

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