题目应该再严谨一点：
lim(x→+∞) π/2-arctan√(2x+1)
=π/2 - lim(x→+∞) arctan√(2x+1)
换元,t=√(2x+1)>0,x=(t^2-1)/2
=π/2 - lim((t^2-1)/2→+∞) arctant
=π/2 - lim(t→+∞) arctant
=π/2 - π/2
=0
有不懂欢迎追问