若0若0若000又tan x=3tan y则tan(x-y)=(tanx-tany)/(1+tanx*tany)=2tany/(1+3tany*tany)=2/(1/tany+3tany)又1/tany+3tany≥2/根号3则tan(x-y)≤根号3/3则x-y≤π/6即x-y≤30º
若000又tan x=3tan y则tan(x-y)=(tanx-tany)/(1+tanx*tany)=2tany/(1+3tany*tany)=2/(1/tany+3tany)又1/tany+3tany≥2/根号3则tan(x-y)≤根号3/3则x-y≤π/6即x-y≤30º