tan(x/2)为什么等于sinx/(1+cosx)

问题描述:

tan(x/2)为什么等于sinx/(1+cosx)

右边=sin[2(x/2)]/[1+cos2(x/2)]
=2sin(x/2)cos(x/2)/[1+2(cosx/2)^2-1]
=sin(x/2)/cos(x/2)
=tan(x/2)