#### Answer

$x=4$ or $x=5$

#### Work Step by Step

A rational expression is undefined when the value of its denominator is zero. Write and solve an expression where the denominator is zero.
$x^2-9x+20=0$
A product is zero when either factor is zero. Factor the trinomial.
$(x-4)(x-5)$
Solve each factor for zero.
$x-4=0$ or $x-5=0$
Use the addition property of equality to solve both equations for x.
$x-4+4=0+4$ or $x-5+5=0+5$
Simplify.
$x=4$ or $x=5$