4. (1 point) A function is said to have a horizontal asymptote if either the limit at infinity exists or the limit at negative infinity exists. Show that each of the following functions has a horizontal asymptote by calculating the given limit. 15x lim 4 + x2 - 9x +3 6-12x 2x2 + 9 lim + x-4-0 13 + x (13x - 7) 2 3x + 13 5x -4 lim x-4 -0 x- 15 -x-8 lim V x2 +7x - 14- x = _ x-too lim V x2 +7x - 14+x = _