Geometry Vocab Flashcards 1

A complete set of high-frequency high school geometry vocabulary flashcards based on the provided topic list covering basic geometric terms, constructions, tools, triangles, and congruence concepts.

Point

A basic geometric term representing a specific location in space with no dimensions.

Line

A basic geometric term representing a straight one-dimensional figure that extends infinitely in both directions.

Line Segment

A part of a line bounded by two distinct end points.

Ray

A part of a line that starts at a given point and extends infinitely in one direction.

Plane

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

Collinear

Points that lie on the same line.

Coplanar

Points, lines, or geometric figures that lie in the same plane.

Parallel Lines

Lines in a plane that never intersect and maintain a constant distance apart.

Perpendicular Lines

Lines that intersect at a right angle ($90^\circ$).

Intersecting Lines

Lines that share exactly one common point where they cross each other.

Skew Lines

Lines in three-dimensional space that do not intersect and are not coplanar.

Angle

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

Right Angle

An angle whose measure is exactly $90^\circ$.

Acute Angle

An angle whose measure is greater than $0^\circ$ and less than $90^\circ$.

Obtuse Angle

An angle whose measure is greater than $90^\circ$ and less than $180^\circ$.

Straight Angle

An angle whose measure is exactly $180^\circ$.

Adjacent Angles

Two angles that share a common side and a common vertex but do not overlap.

Vertical Angles

A pair of non-adjacent opposite angles formed by two intersecting lines.

Complementary Angles

Two angles whose measures add up to $90^\circ$.

Supplementary Angles

Two angles whose measures add up to $180^\circ$.

Compass

A construction tool used for drawing circles, arcs, and measuring distances.

Straightedge

A construction tool used to draw straight lines without measurement markings.

Perpendicular Bisector

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

Angle Bisector

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

Segment Bisector

A point, segment, ray, or line that divides a line segment into two equal parts.

Midpoint

The point that divides a segment into two congruent segments.

Construction

The accurate drawing of geometric shapes and angles using only a compass and straightedge.

Locus (of points)

A set of points that satisfy a given set of geometric conditions.

Conjecture

A mathematical statement proposed to be true based on observations, but not yet proven.

Postulate

A statement accepted as true without proof in geometry.

Theorem

A statement that has been proven true through a logical sequence of mathematical arguments.

Proof

A logical and deductive demonstration that a mathematical statement or theorem is true.

Converse

A statement formed by switching the hypothesis and conclusion of a conditional statement.

Counterexample

A specific case or example that proves a conjecture or statement is false.

Triangle

A polygon with three sides and three vertices.

Vertex

A point where two edges or line segments meet in a geometric figure.

Side

One of the line segments that form a polygon.

Base

The bottom side or reference side of a geometric figure like a triangle.

Altitude (Height)

The perpendicular segment from a vertex of a triangle to the opposite side or line containing the opposite side.

Median

A segment connecting a vertex of a triangle to the midpoint of the opposite side.

Bisector

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

Perimeter

The total distance around the outside edge of a closed geometric figure.

Equilateral Triangle

A triangle with all three sides congruent to each other.

Isosceles Triangle

A triangle with at least two congruent sides.

Scalene Triangle

A triangle in which all three sides have different lengths.

Right Triangle

A triangle containing one right angle ($90^\circ$).

Hypotenuse

The longest side of a right triangle, located opposite the right angle.

Leg

Either of the two sides that form the right angle in a right triangle.

Exterior Angle

An angle formed by one side of a triangle and the extension of an adjacent side.

Triangle Inequality Theorem

A theorem stating that the sum of the lengths of any two sides of a triangle must be greater than the length of the third side.

Congruent Triangles

Triangles that have the exact same size and shape, with all corresponding sides and angles equal.

Similar Triangles

Triangles that have equal corresponding angles and proportional corresponding side lengths.

Congruent

Having the same size and shape.

Corresponding Parts

Matching sides or matching angles in two congruent or similar geometric figures.

CPCTC (Corresponding Parts of Congruent Triangles are Congruent)

Corresponding Parts of Congruent Triangles are Congruent.

SSS (Side-Side-Side)

A congruence shortcut stating that if three sides of one triangle are congruent to three sides of another, the triangles are congruent.

SAS (Side-Angle-Side)

A congruence shortcut stating that if two sides and the included angle of one triangle are congruent to two sides and the included angle of another, the triangles are congruent.

ASA (Angle-Side-Angle)

A congruence shortcut stating that if two angles and the included side of one triangle are congruent to two angles and the included side of another, the triangles are congruent.

AAS (Angle-Angle-Side)

A congruence shortcut stating that if two angles and a non-included side of one triangle are congruent to the corresponding two angles and non-included side of another, the triangles are congruent.

HL (Hypotenuse-Leg)

A congruence theorem stating that if the hypotenuse and one leg of a right triangle are congruent to the hypotenuse and one leg of another right triangle, the triangles are congruent.

Rigid Motion

A transformation that preserves distance and angle measures, resulting in an image congruent to the original shape.

Reflection

A transformation that flips a figure across a line of reflection.

Translation

A transformation that slides every point of a figure the same distance in the same direction.

Rotation

A transformation that turns a figure around a fixed center point by a specified angle.

Glide Reflection

A rigid motion transformation consisting of a translation followed by a reflection across a line parallel to the direction of translation.