证明等式(三角函数的)
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证明等式(三角函数的)
(1-cosx+sinx)除以(1+sinx+cosx)=sinx除以(1+cosx)
(1-cosx+sinx)除以(1+sinx+cosx)=sinx除以(1+cosx)
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(1-cosx+sinx)/(1+sinx+cosx)=sinx/(1+cosx).将cosx用半角公式
左边=[2sin²(x/2)+2sin(x/2)cos(x/2)]/[2cos²(x/2)+2sin(x/2)cos(x/2)]
=2sin(x/2)[sin(x/2)+cos(x/2)]/ 2cos(x/2)[sin(x/2)+cos(x/2)]
=sin(x/2)/ cos(x/2)
=2sin(x/2)cos(x/2)/cos²(x/2) 再反过来用倍角
=sinx / (1+cosx)
=右边
左边=[2sin²(x/2)+2sin(x/2)cos(x/2)]/[2cos²(x/2)+2sin(x/2)cos(x/2)]
=2sin(x/2)[sin(x/2)+cos(x/2)]/ 2cos(x/2)[sin(x/2)+cos(x/2)]
=sin(x/2)/ cos(x/2)
=2sin(x/2)cos(x/2)/cos²(x/2) 再反过来用倍角
=sinx / (1+cosx)
=右边