Graphs are said to be implicitely defined when their equation is not in the form [math]y=f\left(x\right)[/math] but rather in the form [math]f\left(x,y\right)=c[/math], where c may be zero.[br][br]For more on implicit differentiation check my online book [br]"Flipped Classroom Calculus of Single Variable"[br]https://versal.com/learn/vh45au/