 Polar curve

For a homogeneous polynomial $F$ of degree $d$, its first polar with respect to $[a:b:c]$ is the equation $a{F}_x+b{F}_y+c{F}_z=0$, of degree $d-1$ when this polynomial is nonzero. Every singular point of $V(F)$ lies on every such polar. Polars turn the Bézout's theorem intersection count into bounds on singularities and tangencies. The equation is covariant under a linear change of homogeneous coordinates, by the chain rule.

A polar curve is a graph that represents a relationship between a point in the polar coordinate system defined by its distance from a reference point (the pole) and its angle from a reference direction (usually the positive x-axis). In polar coordinates, a point is represented as \((r, \theta)\), where: - \(r\) is the radial distance from the origin (the pole) to the point.