Chapter 1 Geometry Vocabulary

Geometry vocabulary and formulas from Chapter 1 covering points, lines, planes, segments, and angle relationships.

Point

A location with no size or shape.

Line

Made up of points with no thickness or width.

Line Segment

A measurable part of a line consisting of 2 end points.

Ray

A line the extends indefinitely in 1 direction.

Plane

A flat surface made up of points and extends indefinitely in all directions.

Collinear points

Points that lie on the same line.

Coplanar points

Points that line on the same plane.

Non-coplanar points

Points that don't lie on the same plane.

Congruent segments

2 segments that have the same legth.

Segment Addition Postulate

$$AB + BC = AC$$

Segment Bisector

A segment line, or plane that intersects a segment at its mid point.

Directed line segment

A line segment with an associated direction.

$$x_2 - x_1$$

The "run" of a directed line segment.

$$y_2 - y_1$$

The "rise" of a directed line segment.

Perpendicular lines

2 lines that intersect at a $90^{\circ}$ (right angle) Symbol: $\perp$

Perpendicular Bisector

A line, segment, or ray perpendicular to a segment at its midpoint.

Distance Formula

Formula used to find the distance between 2 points on a coordinate plane: $d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$.

Midpoint Formula

Used to find the mid point between 2 end points: $m = (\frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2})$.

Parallel lines

2 lines in the same plane that never intersect. Symbol: $\parallel$

Angle

The intersection of 2 rays at an end point.

Vertex

The common end of an angle (where the 2 end points meet).

Right angle

An angle measuring $90^{\circ}$.

Acute angle

An angle measuring less than $90^{\circ}$.

Obtuse angle

An angle measuring less than $180^{\circ}$ but more than $90^{\circ}$.

Straight angle

An angle that measures $180^{\circ}$.

Congruent angles

2 angles that have the same measure.

Adjacent angles

2 angles that share a common side and vertex (next to eachother).

Angle Addition Postulate

$$\angle ABC + \angle CBD = \angle ABD$$

Angle Bisector

A line or ray that divides an angle into 2 equal parts.

Vertical angles

2 angles directly across from eachother. Formed by 2 intersecting lines. They are congruent.

Complementary angles

2 angles that add to $90^{\circ}$.

Supplementary angles

2 angles that add to $180^{\circ}$.

Linear Pair

Adjacent angles that are supplementary. Combined, they form a straight line.