Essential Concepts
- A set of lines parallel to a given line passing through a given curve is called a cylinder, or a cylindrical surface. The parallel lines are called rulings.
- The intersection of a three-dimensional surface and a plane is called a trace. To find the trace in the [latex]xy[/latex]-, [latex]yz[/latex]-, or [latex]xz[/latex]-planes, set [latex]z=0[/latex], [latex]x=0[/latex], or [latex]y=0[/latex], respectively.
- Quadric surfaces are three-dimensional surfaces with traces composed of conic sections. Every quadric surface can be expressed with an equation of the form [latex]Ax^2+By^2+Cz^2+Dxy+Exz+Fyz+Gx+Hy+Jz+K=0[/latex].
- To sketch the graph of a quadric surface, start by sketching the traces to understand the framework of the surface.
- Important quadric surfaces are summarized in Figure 8 and Figure 9.
Glossary
- cylinder
- a set of lines parallel to a given line passing through a given curve
- ellipsoid
- a three-dimensional surface described by an equation of the form [latex]\frac{x^2}{a^2}+\frac{y^2}{b^2}+\frac{z^2}{c^2}=1[/latex] all traces of this surface are ellipses
- elliptic cone
- a three-dimensional surface described by an equation of the form [latex]\frac{x^2}{a^2}+\frac{y^2}{b^2}-\frac{z^2}{c^2}=0[/latex] traces of this surface include ellipses and intersecting lines
- elliptic paraboloid
- a three-dimensional surface described by an equation of the form [latex]z=\frac{x^2}{a^2}+\frac{y^2}{b^2}[/latex] traces of this surface include ellipses and parabolas
- hyperboloid of one sheet
- a three-dimensional surface described by an equation of the form [latex]\frac{x^2}{a^2}+\frac{y^2}{b^2}-\frac{z^2}{c^2}=1[/latex] traces of this surface include ellipses and parabolas
- hyperboloid of two sheets
- a three-dimensional surface described by an equation of the form [latex]\frac{z^2}{c^2}-\frac{x^2}{a^2}-\frac{y^2}{b^2}=1[/latex] traces of this surface include ellipses and parabolas
- quadric surfaces
- surfaces in three dimensions having the property that the traces of the surface are conic sections (ellipses, hyperbolas, and parabolas)
- rulings
- parallel lines that make up a cylindrical surface
- trace
- the intersection of a three-dimensional surface with a coordinate plane
