In math, you cannot divide by zero, so the x values where it'll make the denominator zero will have a removable discontinuity.
[tex]4x^2-12x[/tex]
Let's factor.
[tex]4x(x-3)[/tex]
[tex]x=0,3[/tex]
That means that the graph will be undefined at [tex]x=0,3[/tex].
