# B Quadratic Equation with three variables

1. Sep 11, 2017

### Leo Authersh

If a quadratic equation of two variables represents a conic section (planar intersection of a cone), then does a quadratic equation of three variables represent the complete cone?

@fresh_42 @FactChecker @WWGD

2. Sep 11, 2017

### phinds

If you have 3 independent variables, is it still a quadratic equation?

3. Sep 11, 2017

### Staff: Mentor

4. Sep 12, 2017

### Staff: Mentor

No.
The usual terminology is second-degree equation. As already mentioned, a second-degree equation in three variables represents a quadric surface, including spheres, ellipsoids, paraboloids, hyperboloids, cones, and a few other degenerate surfaces (the equation $x^2 + y^2 + z^2 = 0$ represents a single point at the origin.)

@Leo Authersh, please do a little basic research before posting your questions. Also, I have moved several of your threads to the General Math section. They are not questions that pertain to Topology or Analysis.