Learning Target: I can name different types of polygons and identify them based on their features.

 
Categories of Polygons


One polygon can have several different names.

With each name, the classification may become more specific.  It may also identify a different feature.

Example

A four-sided figure is:
  • a quadrilateral.
If one pair of opposite sides is parallel, it is:
  • a quadrilateral and
  • a trapezoid.
If both pairs of opposite sides are parallel and congruent, it is:
  •  a quadrilateral and
  •  a parallelogram.
If it also has four right angles, it is:
  •  a quadrilateral,
  •  a parallelogram and
  •  a rectangle.
If all the sides are also of equal length, it is:
  •  a quadrilateral,
  •  a parallelogram,
  •  a rectangle, and
  •  a square.

The most specific classification in this example is square.  It tells us that the figure has four sides of equal length, opposite sides are parallel and all angles are right angles.


A Model








Classifying Triangles

Triangles may also be classified more than one way.  Some names refer to the length of the sides of a triangle.  Other names refer to the kinds of angles a triangle has.

Triangles - By Sides and By Angles






Let's Practice Together

1.  Is the figure below a rectangle?  Explain.







Your Turn
2.  Is the figure below a parallelogram?  Explain.







3.  The equilateral triangle below can also be called:



A.  scalene
B.  acute
C.  right
D.  obtuse



4.  A square is a type of what?
A.  parallelogram
B.  rhombus
C.  rectangle
D.  all of the above





Check for Understanding
1.  Frank says the triangle below is a right triangle.  Abby says it is an isosceles triangle.  Who is right?  Explain.





2.  Can a rhombus be a rectangle?  Explain.















Answers
1. Yes, it meets the qualifications for a rectangle since it has four right angles and opposite sides parallel and congruent.
2. Yes, a rectangle is a type of parallelogram.
3.  B
4.  D
Check for Understanding
1.  They are both right.  It is a right triangle based on its right angle.  It is an isosceles triangle based on having two congruent sides.
2.  A shape can only be a rhombus and a rectangle if it is a square.