Equivalence Relation in Math: Proving Transitivity

[Dustinsfl]

$$\forall a,b\in \mathbb{Z}$$

$$a\sim b$$ iff. $$\left\vert a-b \right\vert \leq 3$$

I have already shown reflexive and symmetric but not sure on how to show transitive.

I know the definition.

 

[Dick]

Why don't you try to show it's not transitive?