triangle
A polygon with three sides.
square
A quadrilateral with four congruent sides and four right angles.
perimeter
Sum of the lengths of all the sides.
kite
A quadrilateral that has two pairs of adjacent sides that are the same length.
diagonal
A line segment connecting any two nonadjacent vertices of a polygon.
convex
Every line segment connecting interior points that is entirely contained with the figure's interior.
parallelogram
A quadrilateral that has two pairs of opposite sides that are parallel.
rectangle
A quadrilateral with four right angles.
trapezoid
A quadrilateral that has only one pair of opposite sides that are parallel.
equilateral triangle
A triangle with three congruent sides.
polygon
A closed plane figure for which all sides are line segments.
scalene triangle
A triangle with all three sides of different lengths.
concave
A shape or solid which has a "cave" in it.
congruent
Shapes that has the same size.
isosceles triangle
A triangle with two congruent sides.
regular polygon
A polygon whose sides and angles are congruent.
n-gon
A polygon with n sides.
dodecagon
A polygon with 12 sides.
decagon
A polygon with 10 sides.
consecutive sides
Two sides that are adjacent and one after the other.
quadrilateral
A four-sided polygon.
rhombus
A parallelogram with 4 congruent sides.
hexagon
A polygon with 6 sides.
pentagon
A polygon with 5 sides.
octagon
A polygon with 8 sides.
consecutive angles
Two angles that are adjacent and one after the other.
septagon
A polygon with 7 sides.
nonagon
A polygon with 9 sides.
vertex
The point where both rays (sides) of an angle meet.
equilateral triangle
A triangle in which all sides are the same length and all angles are the same size.
right triangle
A triangle that has a right angle. (90 degree angle)
obtuse triangle
A triangle in which one angle is larger than 90 degrees.
acute triangle
A triangle in which all three angles are less than 90 degrees.
isosceles triangle
A triangle in which two sides are the same length and the two base angles have the same measure.
scalene triangle
A triangle in which no two sides are of the same length.
hypotenuse
The longest side of a right triangle, opposite the right angle.
leg (right triangle)
The two sides of a right triangle that form the right angle.
base
The third side of an isosceles triangle, it may not be congruent to the other two sides.
leg (isosceles triangle)
The two sides of an isosceles triangle that are congruent.
equiangular triangle
A triangle in which the three angles are congruent.
adjacent sides
Sides of a triangle that share a vertex.
opposite side
The side across from an angle.
triangle
A polygon with three sides.
vertex angle
The angle opposite the base of an isosceles triangle.
180 degrees
The sum of the interior angles of a triangle.
base angles
The angles opposite the congruent sides of an isosceles triangle.
congruent triangles
Two triangles that are have the same shape and size.
acute angle
An angle that measures less than 90 degrees.
right angle
An angle that measures 90 degrees.
obtuse angle
An angle that measures more than 90 degrees but less than 180 degrees.
straight angle
An angle that measures exactly 180 degrees.
complementary angles
Two angles whose sum of measures is 90 degrees.
supplementary angles
Two angles whose sum of measures is 180 degrees.
vertical angles
A pair of opposite angles formed by two intersecting lines. They are congruent.
adjacent angles
Angles that share a common side and a common vertex.
zero angle
An angle that measures exactly 0 degrees.
vertex
The common endpoint of the two rays that make up an angle.
congruent angles
Angles that have the same measure.
angle
Two rays with a common end point.
sides
The rays that make up an angle.
degree
The unit used to measure angles in geometry (based on 360).
protractor
An instrument used to measure angles.
angle bisector
A ray that divides an angle into two congruent angles.
point
It marks a location and is named by a capital letter; it has no thickness and 0 dimension.
line
An infinite set of points that goes on forever; it has no thickness and it is one dimensional.
plane
A flat surface that goes on forever in two directions; an infinite set of points; it has no thickness and is two dimensional.
space
The set of all points. It is three dimensional.
collinear
Points that lie on the same line.
noncollinear
Points that do not lie on the same line.
coplanar
Points that lie on the same plane.
noncoplanar
Points that do not lie on the same plane.
intersection
The set of points both figures have in common.
segment
Part of a line consisting of two end points and all the points between them.
ray
Part of a line that starts at a particular point and extends infinitely in one direction.
perpendicular
Two lines that intersect to form right angles.
parallel
Lines that do not intersect but are in the same plane.
skew
Lines that are not parallel and do not intersect.
opposite rays
Two rays that share a common endpoint but extends in opposite directions and makes a line.
congruent segments
Segments that have the same length.
midpoint
A point that divides a segment into two congruent segments.
endpoint
Marks the end of a line segment or ray.
segment bisector
A line that divides a segment at its midpoint to form two congruent segments.
perpendicular bisector
A line that passes through the midpoint of a segment and is perpendicular to that segment.
intersecting lines
Two lines that cross at a given point.