Ray

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a part of a line consisting of one endpoint and all the points of a line to one side of that endpoint

Segment

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a part of a line with two endpoints

Line

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a series of points that extends infinitely in opposite directions

Right Angle

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an angle that measures exactly 90°

Parallel Lines

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Lines that lie in the same plane and never cross. They are equidistant from each other at all points.

Vertex

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the common endpoint of two rays or segments

Perpendicular Lines

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lines that cross to form right angles

Point

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an exact location in space

Collinear Points

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points that share the same line

Noncollinear Points

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points that are not together on the same line; a single line cannot be drawn through all of the points

Plane

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a flat surface that extends forever in all directions (the two colors represent two different planes)

Intersecting Lines

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lines that cross at exactly one point

Skew Lines

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Lines that are neither parallel nor intersecting. They lie in different planes.

Angle

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The opening between two rays or segments that share a common endpoint

Degrees

The unit that angles are measured in.

Symbol:  °

Acute angle

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An angle that measures less than 90°

Obtuse angle

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An angle that measures more than 90° and less than 180°

Straight angle

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An angle that measures exactly 180°

Complementary angles

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Angles that add up to 90°

Supplementary angles

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Angles that add up to 180°

Transversal

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A line that crosses two or more other lines

Interior angles

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The angles that are between the two lines that are cut by a transversal

Exterior angles

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Angles on the outside of the two lines that are cut by a transversal

Vertical angles

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Angles that are opposite each other when two lines intersect. Angles b and d are vertical angles in this picture. Vertical angles are congruent.

Acute triangle

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a triangle with three acute angles

Obtuse triangle

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a triangle with one obtuse angle

Right triangle

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a triangle with a right angle

Scalene triangle

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a triangle with no congruent sides

Isosceles triangle

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a triangle with two congruent sides

Equilateral triangle

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a triangle with three congruent sides

Polygon

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closed plane figure with straight sides that do not cross

Quadrilateral

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a four sided polygon

Trapezoid

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a quadrilateral with one pair of parallel sides

Parallelogram

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a quadrilateral with two pairs of parallel sides

Rectangle

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a parallelogram with four right angles

Rhombus

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a parallelogram with four congruent sides

Square

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a parallelogram with four congruent sides and four right angles

Congruent

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same shape and size

Similar

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same shape, but not same size (corresponding sides are proportional)

Triangle

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three sided polygon

Pentagon

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five sided polygon

Hexagon

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six sided polygon

Octagon

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eight sided polygon

Decagon

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ten sided polygon