[tex] \frac{x+6}{x-3} [/tex] is a rational expression, and a rational expression is undefined when its denominator is zero. So, to find for what values of [tex]x[/tex] our rational expression is undefined, we are going to set up its denominator equal to zero and solve for [tex]x[/tex]:
[tex]x-3=0[/tex]
[tex]x=3[/tex]
We can conclude that our expression is undefined when [tex]x=3[/tex]. Therefore, 3 is a excluded value for our expression.
