#### Answer

The expression is undefined for $y=-7$ and for $y=7.$

#### Work Step by Step

Rational expressions indicate division and division by zero is undefined.
We must exclude any value or values of the variable that make a denominator zero.
The denominator, $y^{2}-49$ yields zero for
$y^{2}-49=0$
$y^{2}-7^{2}=0$
$(y+7)(y-7)=0,$
for $y=-7$ and for $y=7.$
The expression is undefined for $y=-7$ and for $y=7.$