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point

A fixed location in space.

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line

A straight path that continues without end in both directions.

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line segment

Part of a line between two endpoints.

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ray

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

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intersecting lines

Lines which cross each other, meeting at common point.

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perpendicular lines

Intersecting lines that form right angles.

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parallel lines

Lines in the same plane which do not intersect.

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plane

A flat surface that extends without end in all directions.

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right angle

An angle measuring 90 degrees.

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acute angle

An angle measuring less than 90 degrees.

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straight angle

An angle of 180 degrees.

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obtuse angle

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

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vertex

The endpoint at which two rays intersect.

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protractor

An instrument that is used for constructing and measuring angles.

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equilateral triangle

A triangle with tree sides of equal length.

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isosceles triangle

A triangel with at least two sides of equal length.

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scalene triangle

A triangle having three unequal sides.

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right triangle

A triangle having one 90 degree angle.

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acute triangle

A triangle having three acute angles.

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obtuse triangle

A triangle having one angle greater than 90 degrees.

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polygon

A closed plane figure formed by line segments.

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regular polygon

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

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quadrilateral

A polygon with four sides.

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polyhedron

A solid figure having only flat surfaces called faces.

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circle

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

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compass

A tool used to draw a circle.

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diameter

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

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radius

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

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chord

A line segment with both endpoints on the circle.

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line symmetry

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

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asymmetry

No lines of symmetry exist.

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translation (slide)

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

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reflection (flip)

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

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rotation (turn)

It moves the figure around a fixed point.

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congruent figures

Figures that have the same shape and size.

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similar figures

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

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