求证tan2/x-1/tanx/2=-2/tanx

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求证tan2/x-1/tanx/2=-2/tanx求证tan2/x-1/tanx/2=-2/tanx求证tan2/x-1/tanx/2=-2/tanxtan(x/2)-1/tan(x/2)=sin(x

求证tan2/x-1/tanx/2=-2/tanx
求证tan2/x-1/tanx/2=-2/tanx

求证tan2/x-1/tanx/2=-2/tanx
tan(x/2)-1/tan(x/2)
=sin(x/2)/cos(x/2)-cos(x/2)/sin(x/2)
=sin²(x/2)/sin(x/2)cos(x/2)-cos²(x/2)/sin(x/2)cos(x/2)
=[sin²(x/2)-cos²(x/2)]/[sin(x/2)cos(x/2)]
=-cosx/[(sinx)/2]
=-2/tanx
证毕

加下括号行不?这个有歧义啊