Geometry - Unit 10 Vocabulary

Apex

In a cone or pyramid, the point that is farthest away from the flat surface that contains the base, it is also the place where the lateral faces meet.

Arc

A connected part of a circle.

Cone

A three-dimensional figure that consists of a circular face, called the base, a point called the apex, that is not in the flat surface (plane) of the base, and the lateral surface that connects the apex to each point on the circular boundary of the base.

Cross-section

The intersection of a three dimensional solid and plane.

Cube

A polyhedron all of whose faces are squares.

Dodecahedron

A polyhedron made of twelve pentagons.

Edge

In three dimensions, a line segment formed by the intersection of two faces of a polyhedron.

Equator

Divides the earth into two halves called northern and southern hemispheres.

Great circle

A cross-section of a sphere that has the same radius as the sphere.

Height

The length of the segment that connects the apex to a point in the plan containing the figure's base and its perpendicular to the base.

Icosahedron

A polyhedron made of twenty equilateral triangles.

Lateral face

The triangles formed by connecting consecutive vertices of the base to the apex.

Latitude

An angular measure that indicates how far north or south of the equator a position on the earth is.

Longitude

An angular measure that indicates how far west or east of the prime meridian a position on the earth is.

Meridian

A line of longitude.

Oblique pyramid

A pyramid where the apex is not directly above the center of the base.

Octahedron

A polyhedron made of equilateral triangles that has eight faces.

Platonic solid

A convex polyhedron, all faces are congruent, regular polygons, there are only five possible types - tetrahedron, cube, octahedron, dodecahedron and icosahedron.

Polyhedron

A three-dimensional object with no holes that is bounded by polygons.

Pyramid

A polyhedron with a polygonal base formed by connected each vertex of the base to a single point that is above the flat surface containing the base.

Secant

A line that intersects a circle in two places.

Slant height

The height of the lateral triangular face or cone.

Sphere

The set of all points in space that are the same distance from a fixed point.

Tangent

A line that intersects a circle at exactly one point.

Tetrahedron

Polyhedron made of equilateral triangles that has four faces.

Hemisphere

Half of a sphere, can be created by slicing a sphere with a plane passing through the sphere's center.