Geometry Vocab - Points, Lines, Angles, & Polygons

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Point

A location represented by a dot

Line

An infinate set of points extending endlessly in both directions

Plane

Set of points that form a flat surface that extends infinitely in both directions

Collinear

Points that are on the same line

Non-collinear

Points that are not on the same line

Betweenness

B is between A and C if and only if A, B, C are distinct collinear points and AB + BC = AC

Coplanar

Points that are on the same plane

Parallel Lines

2 lines that never intersect (in same plane)

Perpendicular Lines

2 lines that intersect to form right angles (in same plane)

Line segment

Set of points consisting of two points on a line, called endpoints , and all points on the line between the endpoints

Length/Measure of a Segment

Distance between its endpoints

Congruent Segments

Segments that have the same length/measure

Midpoint

Point on a segment that divides the segments into 2 congruent segments

Bisector of a Segment

Line, ray or a segment that intersects a segment at its midpoint

Ray

Part of a line consisting of an endpoint and extending infinitely in the other direction

Opposite Rays

2 rays of the SAME LINE with a common endpoint.

Angle

The union of 2 rays having the same endpoint (vertex)

Straight Angle

A 180 degree angle (line)

Acute Angle

Between 0 degrees and 90 degrees

Right Angle

A 90 degree angle

Obtuse Angle

between 90 degrees and 180 degrees

Congruent Angles

Two angles that have the same measure

Angle Bisector

Ray whose endpoint is the vertex of the angle and it divides the angle into 2 congruent angles

Complementary Angles

A pair of angles, the sum of whose degree measures 90 degrees

Supplementary Angles

A pair of angles, the sum of whose degree measures 180

Linear Pair

2 adjacent angles whose sum is a straight angle

Vertical Angles

Angles formed across from one another and are congruent

Adjacent Angles

Two angles who share a common vertex, common side (ray), but no common interior points

Polygon

A closed figure in a plane that is the union of line segments such that the segments only intersect at their endpoints and no segments sharing a common endpoint are collinear.

Triangle

A polygon that has exactly 3 sides

Scalene triangle

Triangle that has exactly had no cogruent sides

Isosceles Triangle

Triangle that has 2 congruent sides

Equilateral Triangle

Triangle that has 3 congruent sides

Acute Triangle

Triangle that has 3 acute angles

Equiangular Triangle

Triangle that has 3 congruent angles

Right Triangle

Triangle that has a right angle

Obtuse Triangle

Triangle that has an obtuse angle

Parallel Lines

Lines in the same plane that have no points in common OR all points in common.

Altitude

(height) Line segment drawn from a vertex to the opposite side and is perpendicular to it.

Median

Line segment drawn from a vertex to the midpoint of the opposite side.

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