Introduction to Geometry - Figures

Decagon

A ten sided polygon.

right angle

A 90 degree angle

polygon

A closed plane figure made up of line segments

rectangle

A parallelogram with 4 right angles

parallelogram

A quadrilateral with two pairs of parallel sides

acute angle

An angle less than 90 degrees

obtuse angle

An angle more than 90 degrees

Octagon

An eight sided polygon.

plane

a flat surface that continues forever

diagonal

a line segment connecting any two vertices of a polygon

rhombus

a parallelogram with 4 congruent sides

square

a parallelogram with four congruent sides and four right angles

equilateral polygon

a polygon in which all sides are congruent

convex polygon

a polygon in which each of its diagonals are inside the polygon

regular polygon

a polygon with all sides and all angles equal

concave polygon

a polygon with at least one diagonal outside the polygon

pentagon

a polygon with five sides

quadrilateral

a polygon with four sides

hexagon

a polygon with six sides

triangle

a polygon with three sides

kite

a quadrilateral with two pairs of congruent sides

bisector

a ray, line, line segment, or plane that intersects the segment at its midpoint, a line, ray, segment, or plane that intersects a segment at its midpoint

obtuse triangle

a triangle with an obtuse angle

scalene triangle

a triangle with no two sides of equal length

right triangle

a triangle with one right angle

acute triangle

a triangle with three acute angles

equilateral triangle

a triangle with three congruent sides

isosceles triangle

a triangle with two equal sides

line

defined as having infinite length, but no width or thickness

angle

formed by two rays that share a common endpoint

ray

part of a line with one endpoint

line segment

part of a line with two endpoints