tanx=-2,π/2
问题描述：
tanx=-2,π/2
答
sin(x+π/6) (sin2x+sin^2x)/(1-cos2x)
=sin(x+π/6)(2sinxcosx+sin^2x)/2sin^2x
=[1/2 +cosx/sinx]sin(x+π/6)
=[1/2+1/tanx]sin(x+π/6)
=0
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