题目有错吧,后面应该是[√(x^2+1)-x],而不是[√(x^2+1)-x^2]
limx*[√(x^2+1)-x]
=limx[√(x^2+1)-x][√(x^2+1)+x]/[√(x^2+1)+x]
=limx/[√(x^2+1)+x]
=lim1/{√[1+(1/x)^2]+1}
=1⁄2.