Question

For what value of x is the rational expression below undefined?

Answer 1

The expression is undefined when C, x = 9.

The way that this expression can be undefined is if the denominator is 0 (dividing by 0 is undefined). To make the denominator 0, that means that 9 - x =0. That means that x = 9. So, when x = 9, the denominator is zero, meaning that the expression is undefined when C, x = 9.