A common misunderstanding in Grade 9 about limits is thinking that

$\lim_{x \to a} f(x)$

is the same as just putting $a$ into $f(x)$.

Sometimes this works, but it isn't always true.

This can especially happen if $f(x)$ has a hole or a jump right at $a$.

Another important point is that limits are not the same as actual values.

Limits explain how $f(x)$ behaves as $x$ gets closer to $a$,

but they don't always tell us what happens exactly at $a$.