若0≤x-y＜π/2,且tanx=3tany,则x-y的最大值为?
tan(x-y)=(tanx-tany)/(1+tanxtany)
=2tany/(1+3tan^2y)
=2/(1/tany+3tany)为什么是小于等于这个呢?不懂
≤2/2√(1/tany*3tany)