line
a set of points that extends without end in two opposite directions
ray
a part of a line that has one endpoint and extends without end in one direction
line segment
a part of a line that consists of two endpoints and all the points between them
plane
a flat surface that extends without end in all directions
parallel lines
lines in the same plane that never meet
intersecting lines
lines in a plane that meet at a point
perpendicular lines
when two lines meet at a right angle
angle
a figure formed by two rays with the same endpoint
degree
a unit used to measure angles
right angle
an angle whose measure is exactly 90 degrees
acute angle
an angle whose measure is less than 90 degrees
obtuse angle
an angle whose measure is between 90 and 180 degrees
straight angle
an angle whose measure is exactly 180 degrees
vertical angles
when two lines intersect, the angles opposite each other
complementary angles
two angles whose measures have a sum of 90 degrees
supplementary angles
two angles whose measures have a sum of 180 degrees
triangle
a closed plane figure with three straight sides that connect three points
acute triangle
a triangle with three acute angles
obtuse triangle
a triangle with one obtuse angle
right triangle
a triangle with one right angle
equilateral triangle
a triangle with three sides of the same length
isosceles triangle
a triangle with at least two sides of the same length
scalene triangle
a triangle with three sides of different lengths
quadrilateral
a plane figure formed by four segments called sides. each side intersects exactly two other sides, one at each endpoint, and no two sides are part of the same line
parallelogram
a quadrilateral with two pairs of parallel sides
rectangle
a parallelogram with four right angles
rhombus
a parallelogram with four sides of equal length
square
a parallelogram with four right angles and four sides of equal length
polygon
a closed plane figure that is formed by three or more segments called sides. each side intersects exactly two other sides.
pentagon
a polygon with five sides
hexagon
a polygon with six sides
octagon
a polygon with eight sides
regular polygon
a polygon with equal sides lengths and equal angle measures
diagonal
a segment, other than a side, that connects two vertices of a polygon
similar figures
figures with the same shape but not necessarily the same size
congruent figures
figures with the same size and shape
corresponding parts
the matching sides and angles of two figures
line of symmetry
when a line can be drawn that divides the figure into two congruent parts that are mirror images of each other