Elements of 2D Figures & Classifying Polygons

Point: a position in a plane or in a space that has no dimensions.

Example: a point is written point A.

Line: a set of points in a straight path that extend infinitely in both directions.

This line is named:

AB OR BA A B. .

Line Segment: a portion of a line that has two endpoints.

This line segment is named

AB OR BA

A line segment must be named by its endpoints!

Ray: a portion of a line that extends from one endpoint infinitely in one direction.

The endpoint of the ray is always written first! Any point on the ray may be used next.

Plane: a flat surface that extends infinitely in all directions. Three points that are not collinear (collinear: when three or more points lie on the same line) are needed to determine a plane.

When three or more points that are not collinear lie in the same plane, they are coplanar.

A

B C

Parallel Lines: two lines that never intersect.This symbol means

that the two lines are parallel

Perpendicular Lines: two lines that form a right angle at their point of intersection.

Intersecting Lines: lines that cross each other at exactly one point, which is called the point of intersection.

Point C is the point of intersection of AE and BD

Polygon: Closed plane figure with at least three sides.

Regular Polygon: Polygon with all sides congruent and all angles congruent.

• They are equilateral – sides of equal length• They are equiangular – angles of equal measure.

Irregular Polygon: Polygon whose sides and angles are not all congruent.

PolygonsPolygons Not PolygonsNot Polygons

Line segments are called sides.

Sides meet only at their endpoints.

Points of intersection are called vertices.

Figures whose sides overlap.

Figures that are open.

Figures that have curved sides.

Triangle: 3 sides

Quadrilateral: a four-sided polygon.

Parallelogram: a quadrilateral in which opposite sides are parallel.

squares, rhombuses, and rectangles are all parallelograms.

Pentagon: 5 sides

Hexagon: 6 sides Heptagon: 7 sides

Octagon: 8 sides Nonagon: 9 sides

Decagon: 10 sides

Trapezoid:Quadrilateral

with exactly one pair of parallel sides

RhombusParallelogram with four congruent sides.

RectangleParallelogram

with four right angles

SquareParallelogram

with four right angles and four congruent sides

Determine whether each statement is sometimes, always, or never true.

a. A quadrilateral is a trapezoid.

b. A parallelogram is a rectangle.

c. A trapezoid is a parallelogram.

d. A rhombus is a square.

e. A square is a parallelogram.

f. A parallelogram is a square.

g. A parallelogram is a trapezoid.

h. A square is a quadrilateral.

i. A rhombus is a rectangle.

j. A quadrilateral is a rectangle.