Some math functions have specific limits on what numbers you can use with them. This can make learning challenging for students.

1. Zero in the Denominator: For a function like $f(x) = \frac{1}{x}$, you can't let $x$ be zero. This means we can only use numbers for $x$ that are not zero. Understanding this can be tough.

2. Square Roots and Negative Numbers: With the function $g(x) = \sqrt{x}$, the input must be a number that is zero or bigger. This means we can only use numbers in the range of $[0, \infty)$. Students can get confused if they forget this rule.

3. Trigonometric Functions: Functions like sine wave back and forth, but they only go between $-1$ and $1$. This can limit the possible outputs or range.

To help students with these concepts, teachers should encourage them to look closely at how functions work. Drawing graphs can also help students see where the limits are for the input and output of these functions.