Deletion of Derivation of the Cartesian form for an ellipse

Comment: I notice that this seems to be part of an ongoing edit war at Ellipse (see https://en.wikipedia.org/w/index.php?title=Ellipse&action=history). I https://en.wikipedia.org/w/index.php?title=Ellipse&type=revision&diff=730340724&oldid=730320708 added http://nebula.deanza.edu/~bloom/math43/ellipse-derivation.pdf this external link at the relevant place in Ellipse#Equations, so I do not think there is anything else to do. (The source looks shaky, but it's totally non- standard math
Stance: delete
Cited policy: Wikipedia:Verifiability (WP:EXTRAORDINARY)