Search results
Results From The WOW.Com Content Network
Often, the degenerate cases are the exceptional cases where changes to the usual dimension or the cardinality of the object (or of some part of it) occur. For example, a triangle is an object of dimension two, and a degenerate triangle is contained in a line , [ 3 ] which makes its dimension one.
This case always occurs as a degenerate conic in a pencil of circles. However, in other contexts it is not considered as a degenerate conic, as its equation is not of degree 2. The case of coincident lines occurs if and only if the rank of the 3×3 matrix is 1; in all other degenerate cases its rank is 2. [3]: p.108
Let line L be the polar line of point p with respect to the non-degenerate conic Q. By La Hire's theorem, every line passing through p has its pole on L. If L intersects Q in two points (the maximum possible) then the polars of those points are tangent lines that pass through p and such a point is called an exterior or outer point of Q.
Conic Section(s) Unit Circle: Unit Hyperbola: Degree 3: Folium of Descartes: Cissoid of Diocles: Conchoid of de Sluze: Right Strophoid: Semicubical Parabola: Serpentine Curve: Trident Curve: Trisectrix of Maclaurin: Tschirnhausen Cubic: Witch of Agnesi: Degree 4: Ampersand Curve: Bean Curve: Bicorn: Bow Curve: Bullet-Nose Curve: Cruciform Curve
A special case is Pascal's theorem, in which case the two cubics in question are all degenerate: given six points on a conic (a hexagon), consider the lines obtained by extending opposite sides – this yields two cubics of three lines each, which intersect in 9 points – the 6 points on the conic, and 3 others. These 3 additional points lie ...
In algebraic geometry, the conic sections in the projective plane form a linear system of dimension five, as one sees by counting the constants in the degree two equations. The condition to pass through a given point P imposes a single linear condition, so that conics C through P form a linear system of dimension 4.
To distinguish the degenerate cases from the non-degenerate cases (including the empty set with the latter) using matrix notation, let β be the determinant of the 3 × 3 matrix of the conic section—that is, β = (AC − B 2 / 4 )F + BED − CD 2 − AE 2 / 4 ; and let α = B 2 − 4AC be the discriminant.
The reason each line is assumed to contain at least 3 points is to eliminate some degenerate cases. The spaces satisfying these three axioms either have at most one line, or are projective spaces of some dimension over a division ring , or are non-Desarguesian planes .