I'm working on the following problem:
$$ r^4 - 3r^2 -4r = 0 $$
I factor out one $r$ and leaving me $ r(r^3 - 3r -4) = 0 $. One real root is $r=0$, and I'm unable to find the other ones. I tried using synthetic division but it didn't help. I tried googling synthetic division with complex root problems, but all the videos use examples that are given a complex solution in order to solve the other roots. So what could be a good approach in this problem?