algebra precalculus - Solve $x = y^{2} - y$ for $y$

Make y the subject of $x=y^2-y$

I put this into Wolfram Alpha and it said the answer was $(1\pm\frac{\sqrt{4x+1}}{2})$ but I have absolutely no idea how it got to that answer, so I'd appreciate if someone could explain it to me, thanks in advance.