A rational expression is undefined when the denominator is equal to zero. To find the values that make a rational expression undefined, set the denominator equal to zero and solve the resulting equation.

Is a denominator of 0 undefined?

if we ever have 0 in the denominator, all we can say is that the fraction is “undefined.”

Why is denominator 0 undefined?

Again, any number multiplied by 0 is 0 and so this time every number solves the equation instead of there being a single number that can be taken as the value of 00. In general, a single value can't be assigned to a fraction where the denominator is 0 so the value remains undefined.