First write the function [tex]y=(x+12)(x-6)[/tex] in standard form [tex]y=ax^2+bx+c:[/tex]
[tex]y=x^2-6x+12x-72,\\\\y=x^2+6x-72.[/tex]
Find the x-coordinate according to the rule
[tex]x_{vertex}=-\dfrac{b}{2a}.[/tex]
Thus,
[tex]x_{vertex}=-\dfrac{6}{2\cdot 1}=-3.[/tex]
Now find the y-coordinate of the vertex substituting x=-3 into the parabola equation:
[tex]y_{vertex}=(-3)^2+6\cdot (-3)-72=9-18-72=-81.[/tex]
Answer: the x-coordinate if the vertex is -3.
