###
acute angle

An angle that measures less than 90 degrees.

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acute triangle

A triangle with all angles measuring less than 90 degrees.

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angle

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

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complementary angle

Two angles whose measures add to 90 degrees.

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congruent

Figures with the same size and shape.

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correspondence

The relationship between two or more objects that are matched.

###
equilateral triangle

A triangle with three congruent sides.

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isoscleles triangle

A triangle with at least two congruent sides.

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line

A straight path that extends without end in opposite directions.

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line symmetry

One half of a figure is a mirror image of the other half.

###
line of symmetry

The imaginary line drawn down the center of a figure with line symmetry.

###
obtuse angle

An angle whose measure is greater than 90 degrees.

###
obtuse triangle

A triangle containing one obtuse angle.

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parallel lines

Lines in a plane that never intersect.

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parallelogram

A quadrilateral with two pairs of parallel sides.

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perpendicular lines

Lines that intersect to form right angles.

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plane

A flat surface that extends forever.

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point

An exact location in space.

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polygon

A closed figure formed by three or more line segments that intersect only at their endpoints.

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ray

A part of a line that starts at one endpoint and extends forever in one direction.

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rectangle

A parallelogram with four right angles.

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reflection

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

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regular polygon

A polygon with congruent sides and angles.

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regular tessellation

A regular polygon is repeated to fill a plane.

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rhombus

A parallelogram with all sides congruent.

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right angle

An angle that measures 90 degrees.

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right triangle

A triangle containing a right angle.

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rotation

A transformation in which a figure is turned around a point.

###
rotational symmetry

A figure can be rotated less than 360 degrees around a central point and coincide with the original figure.

###
scalene triangle

A triangle with no congruent sides.

###
segment

A part of a line between two endpoints.

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square

A rectangle with four congruent sides.

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supplementary angles

Two angles whose measures have a sum of 180 degrees.

###
tesselation

A repeating pattern of plane figures that completely cover a plane with no gaps or overlaps.

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transformation

A change in the size or position of a figure.

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translation

A movement of a figure along a straight line.

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transversal

A line that intersects two or more lines.

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trapezoid

A quadrilateral with exactly one pair of parallel sides.

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Triangle Sum Theorem

The theorem that states that the measures of the angles in a trianlge add up to 180 degrees.

###
vertical angles

A pair of opposite congruent angles formed by intersecting lines.

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corresponding angles

Angles formed by a transversal cutting through 2 or more lines that are in the same relative position.

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quadrilateral

A four sided figure

###
pentagon

A five sided figure

###
hexagon

A six sided figure

###
heptagon

A seven sided figure

###
octagon

An eight sided figure

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