Geometry Unit 1 Glossary

Geometry Vocabulary Flashcards for Unit 1

Point

Indicates a position and has no size.

Line

A straight arrangement of points extending infinitely in opposite directions.

Plane

A flat two-dimensional surface that extends forever.

Intersecting lines

When two lines share a common point.

Collinear

Points that lie on the same line.

Coplanar

Points that exist on the same plane.

Spherical geometry

The study of geometry on the surface of a sphere.

Euclidean geometry

A mathematical system with theorems and postulates deduced from axioms, attributed to Euclid.

Undefined terms

Points, lines, and planes are these.

Postulate

A statement accepted as true without proof.

Theorem

A statement that can be proven true.

Line Segment

Part of a line with two endpoints and all points in between.

Ray

Part of a line starting at a point and extending infinitely in one direction.

Opposite Rays

Two rays with a common endpoint that form a line.

Angle

The figure formed by two rays with a common endpoint.

Acute Angle

Angles with measures less than 90°.

Obtuse Angle

Angles measuring greater than 90° but less than 180°.

Right Angle

Angles that measure 90°.

Midpoint

Divides a segment into two congruent segments and lies on the segment itself.

Angle Bisector

A line, segment, or ray that divides an angle into two congruent angles.

Perpendicular Lines

Lines that intersect to form four right angles.

Parallel Lines

Coplanar lines that never intersect.

Skew Lines

Non-parallel, non-intersecting lines that do not exist in two dimensions.