How do you know if a limit is undefined?

The answer to your question is that the limit is undefined if the limit does not exist as described by this technical definition. ... In this example the limit of f(x), as x approaches zero, does not exist since, as x approaches zero, the values of the function get large without bound.

How do you know when a function is undefined?

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. Example: 0 7 2 3 x x − Is undefined because the zero is in the denominator.