I've been studying quasi-projective varieties, and on the Wikipedia page it says the complement of a conic in $\mathbb{P}^2$ is affine, but it does not justify it or say what it is isomorphic to (or give a citation). I'm trying to figure out how that's true.
I know that to be affine it must be isomorphic to a Zariski-closed set, but what is the complement of a conic isomorphic to?