The equation is f(x) =(x-6*(x+6))/(x^2 - 9).
For the vertical asymptote test in a rational function. The denominator is first set to zero.
x^2 - 9 = 0
x^2 = 9
x = +-3
The values for x are then substituted to the numerator.
x=3; x-6(x+6) = 3-6(3+6) = -51
x=-3; x-6(x+6) = -3-6(-3+6)= -21
The zeros of the denominator do not make the numerator zero so the vertical asymptotes are x= +-3
