→+∞
lim √(4r^2+1)-2r
=lim √(4r^2+1)-√(4r^2)
=lim (√(4r^2+1)-√(4r^2))(√(4r^2+1)+√(4r^2))/(√(4r^2+1)+√(4r^2))
=lim 1 / (√(4r^2+1)+√(4r^2))
=0
有不懂欢迎追问
R趋近于正无穷 lim√（4R^2+1）-2R
→+∞
lim √(4r^2+1)-2r
=lim √(4r^2+1)-√(4r^2)
=lim (√(4r^2+1)-√(4r^2))(√(4r^2+1)+√(4r^2))/(√(4r^2+1)+√(4r^2))
=lim 1 / (√(4r^2+1)+√(4r^2))
=0
有不懂欢迎追问