(4)lim [√(x²+1)-√(x²-1)]x→∞=lim [√(x²+1)-√(x²-1)][√(x²+1)+√(x²-1)]/[√(x²+1)+√(x²-1)]x→∞=lim [(x²+1)-(x²-1)]/[√(x²+1)+√(x²-1)]x→∞=lim 2/[√(x²+1)+√(x²-1)]x→∞=lim (2/|x|)/[√(1+ 1/x²)+√(1- 1/x²)]x→∞=0/[√(1+0)+√(1-0)]=0/2=0