求证tanx/2-1/（tanx/2）=-2/tanx
问题描述：
求证tanx/2-1/（tanx/2）=-2/tanx
答
求证tanx/2-1/（tanx/2）=-2/tanx
证：左边 = (sin x/2)/(cos x/2) - (cos x/2)/(sin x/2)
=[(sin x/2)^2 - (cos x/2)^2 ]/(cos x/2)(sin x/2)
=-2cosx/sinx
=-2/tanx = 右边
即等式得证.