#### Answer

$y=5$ or $y=-5$

#### 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.
$y^2-25=0$
A product is zero when either factor is zero. Factor the binomial.
$(y-5)(y+5)$
Solve each factor for zero.
$y-5=0$ or $y+5=0$
Use the addition property of equality to solve both equations for y.
$y-5+5=0+5$ or $y+5-5=0-5$
Simplify.
$y=5$ or $y=-5$