Can we make a non-regular language regular via concatentation?
Yes this is possible. Consider the example given below:

Let $B = 1^p$ where $p$ is prime. This is non regular.
Let $A = 1^n$ where $n \in \mathbb{N}$. This is regular.

$AB$ will simply give us $1^n$ with $n &gt; 2$ and this is regular since any number greater than $2$ can be reprsent as $2+x$ where $x &gt; 0$