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acute triangle

a triangle whose interior angles are all acute

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altitude

the perpendicular distance from the base of a geometric figure to opposite vertex (or side if parallel)

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complementary angles

two angles whose measures have a sum of 90 degrees

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congruent

having the same size and shape

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edge

the line segment where two faces of a solid figure meet

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equilateral triangle

a triangle with three congruent sides

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perpendicular lines

lines that intersect at one point and form right angles

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perimeter

the distance around a 2-dimensiional figure

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area

the number of square units needed to cover a surface

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right angle

an angle with a measure of 90 degrees

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straight angle

an angle whose measure is 180 degrees

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obtuse angle

an angle with a measure of more than 90 degrees but less than 180 degrees

###
acute angles

angles that measures greater than 0 degrees and less than 90 degrees

###
exterior angles

angles on the outer sides of two lines cut by a transversal

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face

a flat surface of a polyhedron

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hypotenuse

in a right triangle, the side opposite the right angle

###
interior angles

angles on the inner sides of two lines that cut by a transversal

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intersecting lines

two lines that cross at exactly one point

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isosceles triangle

a triangle with two congruent sides

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line

a straight path that extends infinitely in opposite directions

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line segment

part of a line with two endpoints

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line symmetry

a type of symmetry in which a line divides a figure into two congruent parts that are mirror images

###
obtuse triangle

a triangle with one obtuse angle

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parallell lines

two lines in the same plane that never intersect

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parallelogram

a quadrilateral with opposite sides parallel and congruent

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perpendicular bisector

line that intersects a line segment at its midpoint and forms right angles

###
plane

a flat surface that extends infinitely in all directions

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polygon

a closed plane figure made of line segments

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prism

a polyhedron with two parallel, congruent bases; all other faces of the prism are parallelograms

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pyramid

a 3-dimensional shape whose base is a polygon and whose triangular faces meet at a single point

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Pythagorean Theorem

the square of the hypotenuse (c) of a right triangle is equal to the sum of the squares of the legs (a and b)

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quadrilateral

a four-sided polygon

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radius

a line segment with one endpoint at the center of a circle and the other endpoint on the circle

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ray

part of a line that has one endpoint and extends forever in the other direction

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reflection

a transformation that produces a mirror image of a geometric figure (flip)

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regular polygon

a polygon in which all sides are the same length and all angles have the same measure

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rhombus

a parallellogram whose four sides are congruent and whose opposite angles are congruent

###
supplementary angles

two angles whose sum equals 180 degrees

###
sphere

a three-dimensional shape with all points on the surface equidistant from the center

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scalene triangle

a triangle with no congruent sides

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rotation

a transformation of a figure by turning it about a fixed point called the center of rotation or axis

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right triangle

a triangle with one right angle

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tessellation

a pattern of congruent shapes covering a surface without gaps or overlap

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transformation

a change in size, shape, of position of a geometric figure

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translation

a transformation that moves a geometric figure by sliding each of the points the same distance in the same direction

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vertex

a point where 2 rays meet, where two sides of a polygon meet or where the edges of a polyhedron meet; the top point of a cone or pyramid

###
vertical angles

a pair of opposite congruent angles formed by two intersecting lines

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volume

the number of cubic units needed to fill the space occupied by a solid

### Flickr Creative Commons Images

Some images used in this set are licensed under the Creative Commons through Flickr.com. Click to see the original works with their full license.