tan1／2θ－tan1／2θ／1＝－2／tanθ求证

tan1／2θ－tan1／2θ／1＝－2／tanθ求证
tan1／2θ－tan1／2θ／1＝－2／tanθ求证

tan1／2θ－tan1／2θ／1＝－2／tanθ求证
令a=1／2θ
左边=tana-1/tana
=(tan²a-1)/tana
=-2/[2tana/(1-tan²a)]
=-2/tan2a
=－2／tanθ