lim(x→∞)x[√(1+x^2)-x]
=lim(x→∞){x(1+x^2-x^2)/[√(1+x^2)+x]}
=lim(x→∞){x/[√(1+x^2)+x]}
=lim(x→∞){1/[√(1+1/x^2)+1]}
=1/[√(1+0)+1]
=1/2
lim(x→∞)x[√(1+x^2)-x]
=lim(x→∞){x(1+x^2-x^2)/[√(1+x^2)+x]}
=lim(x→∞){x/[√(1+x^2)+x]}
=lim(x→∞){1/[√(1+1/x^2)+1]}
=1/[√(1+0)+1]
=1/2