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Acute angle
an angle that measures less than 90°
Acute triangle
a triangle with all angles measuring less than 90°
Adjacent angles
angles in the same plane that have a common vertex and a common ray
Angle
a figure formed by 2 rays with a common endpoint called the vertex
Complementary angles
two angles whose measures add up to 90°
Congruent angles
angles that have the same measure
Equilateral triangle
a triangle
Isosceles triangle
a triangle with at least two congruent sides
Line
a straight path that extends without end in opposite directions
Line of reflection
a line that a figure is flipped across to create a mirror image of the
original figure
Line of symmetry
the imaginary “mirror” in line symmetry
Line segment
a part of a line between two endpoints
Line symmetry
a figure has line symmetry if one half is a mirror-image of the other half
Obtuse angle
an angle whose measure is greater than 90° but less than 180°
Obtuse triangle
a triangle containing one obtuse angle
Parallel lines
lines in a plane that do not intersect
Parallelogram
a quadrilateral with two pairs of parallel sides
Perpendicular lines
lines that intersect to form right angles
Plane
a flat surface that extends forever
Point
an exact location in space
Polygon
a closed plan e figure formed by three or more line segments that
intersect only at their endpoints
Quadrilateral
a four-sided polygon
Ray
a part of a line that starts at one endpoint and extends forever
Rectangle
a parallelogram with four right angles
Reflection
a transformation of a figure that flips the figure across a line
Regular polygon
a polygon with congruent sides and angles
Rhombus
a parallelogram with all sides congruent
Right angle
a triangle containing a right angle
Right triangle
a triangle containing a right angle
Rotation
a transformation in which a figure is turned around a point
Scalene triangle
a triangle with no congruent sides
Skew lines
lines that lie in different planes that are neither parallel nor intersecting
Square
a rectangle with four congruent sides
Straight angle
an angle that measures 180°
Supplementary angles
two angles whose measures have a sum of 180°
Transformation
a change in the size or position of a figure
Translation
a movement (slide) of a figure along a straight line
Trapezoid
a quadrilateral with exactly one pair of parallel sides
Vertical angles
a pair of opposite congruent angles formed by intersecting lines
Vertex
on an angle or polygon, the point where two sides intersect