Basic Geometry Terms

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Hypotenuse
longest side in a right triangle; opposite the right angle
Octagon
8-sided polygon
Scalene Triangle
triangle with no sides equal in length
Hexagon
6-sided polygon
Line Segment
part of a line with two endpoints
Vertex
point where two rays meet
Perpendicular Lines
lines that intersect to form four right angles
Decagon
10-sided polygon
Quadrilateral
4-sided polygon
Equilateral Triangle
triangle with all sides equal in length
Diagonal
connects two non-consecutive vertices
Line
a collection of points extending forever in opposite directions
Triangle
3-sided polygon
Point
an exact location in space
Ray
contains an endpoint and extends forever in the opposite direction
Parallel Lines
two lines that never intersect and are always the same distance apart
Nonagon
9-sided polygon
Pentagon
5-sided polygon
Right Triangle
a triangle that contains a right angle
Isosceles Triangle
a triangle with two sides equal in length
Legs
the two sides of a right triangle that meet to form the right angle
Square
a quadrilateral with 4 equal sides and 4 right angles
Rectangle
a quadrilateral with 4 right angles and opposite sides are parallel and equal in length
Right angle
an angle that is 90 degrees
Trapezoid
a quadrilateral with one pair of parallel sides
Angle
two rays with the same endpoint
Rhombus
a quadrilateral with 4 equal sides and opposite angles equal
Complementary angles
two angles whose sum is 90 degrees
Supplementary angles
two angles whose sum is 180 degrees
Adjacent angles
two angles that share a vertex and a common side, but have no common interior points
Obtuse angles
angles whose measure is greater than 90 degrees and is less than 180 degrees
Straight angles
an angle whose measure is 180 degrees
Vertical angles
two nonadjacent angles formed by two intersecting lines
Transversal
a line that cuts across a set of lines or the sides of a plane figure
Symmetric
a geometric figure or graph consisting of two parts that are congruent to each other
Skew lines
lines in three dimensional space that do not intersect and are not parallel
Diameter
a line segment between two points on a circle or sphere which passes through the center
Radius
a line segment between the center and a point on the circle or sphere
Circumference
the distance around the outside of a circle
Plane
a flat surface that can extend forever in length and width, but has no thickness
Coplanar
points or lines that all lie in the same plane
Congruent
planar figures or solid shapes that have the same shape and size
Alternate interior angles
either pair of interior angles lying on opposite sides of the transversal
Alternate exterior angles
either pair of exterior angles lying on opposite sides of the transversal
Corresponding angles
two angles which occupy the same position, such as angles 1 and 5
Acute angle
an angle whose measure is less than 90 degrees
parallelogram
a 4 sided polygon with both pairs of opposite sides equal and opposite angles equal

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