Geometry Basics: Points, Lines, Planes & Angle Relationships

Vocabulary flashcards summarizing key definitions, formulas, and angle relationships from Sections 1.1 to 1.4.

Point

A location in space that has no size or dimension.

Line

A straight path extending infinitely in both directions; one-dimensional.

Plane

A flat surface that extends infinitely in all directions; two-dimensional.

Collinear

Points that lie on the same line.

Coplanar

Points that lie on the same plane.

Line Segment

A part of a line bounded by two endpoints.

Congruent Segments

Line segments that have equal length.

Midpoint

The point that divides a segment into two congruent parts.

Segment Bisector

A point, line, ray, or segment that intersects a segment at its midpoint, cutting it in half.

Midpoint Formula

M = ( (x₁ + x₂)⁄2 , (y₁ + y₂)⁄2 ) — finds the midpoint between two coordinate points.

Distance Formula

d = √[(x₂ − x₁)² + (y₂ − y₁)²] — calculates the distance between two points in the coordinate plane.

Angle

A figure formed by two rays sharing a common endpoint called the vertex.

Right Angle

An angle that measures exactly 90°.

Acute Angle

An angle that measures less than 90°.

Obtuse Angle

An angle that measures more than 90° but less than 180°.

Straight Angle

An angle that measures exactly 180°.

Adjacent Angles

Two angles that share a common vertex and side but have no interior points in common.

Vertical Angles

Opposite angles formed by two intersecting lines; they are always congruent.

Linear Pair

A pair of adjacent angles whose non-common sides form a straight line; the angles are supplementary.

Complementary Angles

Two angles whose measures add up to 90°.

Supplementary Angles

Two angles whose measures add up to 180°.