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acute triangle

a triangle whose interior angles are all acute

complementary angles

two angles whose measures have a sum of 90 degrees


having the same size and shape

equilateral triangle

a triangle with three congruent sides

perpendicular lines

lines that intersect at one point and form right angles

right angle

an angle with a measure of 90 degrees

straight angle

an angle whose measure is 180 degrees

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


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

intersecting lines

two lines that cross at exactly one point

isosceles triangle

a triangle with two congruent sides


a straight path that extends infinitely in opposite directions

line segment

part of a line with two endpoints

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

parallell lines

two lines in the same plane that never intersect


a quadrilateral with opposite sides parallel and congruent


a closed plane figure made of line segments


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


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


a four-sided polygon


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


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

regular polygon

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


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

supplementary angles

two angles whose sum equals 180 degrees


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

scalene triangle

a triangle with no congruent sides


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

right triangle

a triangle with one right angle


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


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

vertical angles

a pair of opposite congruent angles formed by two intersecting lines

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