已知:tanx=-2,求:(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)想知道这步(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)是怎么变成(cosx-sinx)/(cosx+sinx)这步的!在线等~
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![已知:tanx=-2,求:(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)想知道这步(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)是怎么变成(cosx-sinx)/(cosx+sinx)这步的!在线等~](/uploads/image/z/3860960-32-0.jpg?t=%E5%B7%B2%E7%9F%A5%3Atanx%3D-2%2C%E6%B1%82%3A%282cos%5E2%28x%2F2%29-sinx-1%29%2F%E6%A0%B9%E5%8F%B72sin%28%CF%80%2F4%2Bx%29%E6%83%B3%E7%9F%A5%E9%81%93%E8%BF%99%E6%AD%A5%282cos%5E2%28x%2F2%29-sinx-1%29%2F%E6%A0%B9%E5%8F%B72sin%28%CF%80%2F4%2Bx%29%E6%98%AF%E6%80%8E%E4%B9%88%E5%8F%98%E6%88%90%28cosx-sinx%29%2F%28cosx%2Bsinx%29%E8%BF%99%E6%AD%A5%E7%9A%84%21%E5%9C%A8%E7%BA%BF%E7%AD%89%7E)
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已知:tanx=-2,求:(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)想知道这步(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)是怎么变成(cosx-sinx)/(cosx+sinx)这步的!在线等~
已知:tanx=-2,求:(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)
想知道这步(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)是怎么变成(cosx-sinx)/(cosx+sinx)这步的!
在线等~
已知:tanx=-2,求:(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)想知道这步(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)是怎么变成(cosx-sinx)/(cosx+sinx)这步的!在线等~
由倍角公式 cos²x=2cos²(x/2)-1,可得
2cos^2(x/2)-sinx-1=cosx-sinx
由和角公式,可得
√2sin(π/4+x)=√2(sinxcosπ/4+cosxsinπ/4)=sinx+cosx
所以,
(2cos^2(x/2)-sinx-1)/根号2sin(π/4+x)
=(cosx-sinx)/(cosx+sinx)
=(1-tanx)/(1+tanx)
=(1+2)/(1-2)
=-3