Recursion is where a function is defined based on itself.

For instance, $f(x)=\left\{ \begin{array}{} f(x)-1\text{ if }x≤0\\ \text{else }x\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ \end{array} \right.$is recursive because f(x) is defined on x.

<aside> ❓ What do you think is $f(10)$?

</aside>

• Answer

Remember that a good recursion function should stop at some point.

$f(x)=f(x-1)+1$ is not good enough because $f(10)=f(9)+1=f(8)+2=...=f(-100)+110=...$ goes on and on forever.