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point

A fixed location in space.

line

A straight path that continues without end in both directions.

line segment

Part of a line between two endpoints.

ray

Part of a line that has one endpoint and goes on without end in one direction.

intersecting lines

Lines which cross each other, meeting at common point.

perpendicular lines

Intersecting lines that form right angles.

parallel lines

Lines in the same plane which do not intersect.

plane

A flat surface that extends without end in all directions.

right angle

An angle measuring 90 degrees.

acute angle

An angle measuring less than 90 degrees.

straight angle

An angle of 180 degrees.

obtuse angle

An angle measuring greater than 90 degrees but less than 180 degrees.

vertex

The endpoint at which two rays intersect.

protractor

An instrument that is used for constructing and measuring angles.

equilateral triangle

A triangle with tree sides of equal length.

isosceles triangle

A triangel with at least two sides of equal length.

scalene triangle

A triangle having three unequal sides.

right triangle

A triangle having one 90 degree angle.

acute triangle

A triangle having three acute angles.

obtuse triangle

A triangle having one angle greater than 90 degrees.

polygon

A closed plane figure formed by line segments.

regular polygon

Has sides that are equal in length and angles that are equal in size.

quadrilateral

A polygon with four sides.

polyhedron

A solid figure having only flat surfaces called faces.

circle

A closed plane figure with all points an equal distance from the center.

compass

A tool used to draw a circle.

diameter

A line segment crossing the center of a circle and having both endpoints on the circle.

radius

A line segment from the center to a point on the circle.

chord

A line segment with both endpoints on the circle.

line symmetry

A line (or fold) that divides a figure into congruent halves.

asymmetry

No lines of symmetry exist.

translation (slide)

It moves the figure in a straight line, changing its location, but not its position.

reflection (flip)

A move that turns the figure over on a line of symmetry.

rotation (turn)

It moves the figure around a fixed point.

congruent figures

Figures that have the same shape and size.

similar figures

Figures that have the same shape but may not have the same size.