For the curve $x^3+xy^2+4xy=0$, I know you can break it up into $x=0$ and $x^2+y^2+4y=0$ by factorising, both of which are very standard functions. However when I plug the equation into Desmos I get:
Why does the line $x=0$ get cut off by the circle? Shouldn't the whole $y$-axis be in red?