Imagine we have the triangle below. This is just a generic triangle. Pretend we only know the two side lengths. None of the angles. We don't even know what it looks like.

What are the Possible Side Lengths of $y$?

Well, there are an infinite number of possibilities. Fortunately, they can be represented by an inequality produced by this formula.

$$(9-5) < y <(9+5)$$

$$4 < y <14$$

Side length $y$ must be larger than $4$ and smaller than $14$. If we consider only integer values for $y$, it must be either $5$, $6$, $7$, $8$, $9$, $10$, $11$, $12$, or $13$.

For any generic triangle, the unknown side must be larger than the difference of the other two sides and smaller than their sum.