# Chapter 18 Two-Dimensional Shapes

• Chapter 18

Chapter Objective:

* Polygons can be classified by the number of sides, corners and angles. Figures can be congruent or symmetrical, or both.

Vocabulary:

plane figure - A plane figure is a flat figure. It can be open or closed.

open figure - An open figure is a plane figure that does not start and end at the same point; the figure is 'open' and not closed.

closed figure - A closed figure is a figure that starts and ends at the same point; the figure is 'closed' and not left open.

polygon - A polygon is a closed plane figure that is formed with three or more line segments.

vertex - A vertex is a point where two sides of a polygon meet.

quadrilateral - A quadrilateral is a polygon that has four sides and four angles.

parallel - Parallel refers to lines that will never meet, no matter how long they are drawn. The lines will always have the same distance between them.

rhombus - A rhombus is a parallelogram that has four sides of equal length.

parallelogram - A parallelogram is a quadrilateral with two pairs of opposite sides that are parallel. Only the opposite sides of a parallelogram need to be equal in length.

pentagon - A pentagon is a polygon that has five sides.

octagon - An octagon is a polygon that has eight sides.

tangram - A tangram is made up of seven polygons that can be put together to make a square.

slide - When you slide a a figure, it can be slid in any direction to a new position.

flip - When you flip a figure, you turn a shape front to back over a line.