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}

=12.