lim(x→π/2) tanx/tan(3x)
＝lim(x→π/2) [sinx/sin(3x)×cos(3x)/cosx]
＝－lim(x→π/2) cos(3x)/cosx洛必达法则
＝－lim(x→π/2) 3sin(3x)/sinx
＝3