Reason for Alignment: Quadrilaterals is designed to introduce students to quadrilaterals through discussions of parallelograms, rectangles, and trapezoids. The worksheet associated with this lesson is particularly helpful with the definitions of the various kinds of quadrilaterals. This lesson provides extra practice with all the vocabulary that goes with geometry. This lesson is a reinforcement of key terms and concepts from the textbook.
Try an example with your students, letting the students direct your moves.
Ask the students to help you create a trapezoid from the square on the screen. As they direct
your moves, have them specify which characteristic of the trapezoid they are attempting to
When the class is satisfied with the trapezoid that has been created, show them how to gain
information about the quadrilateral from the
Allow the students to comment on how they think the information shows that the quadrilateral
is a trapezoid. Students should recognize that it is necessary to show that two of the lines
in the quadrilateral are parallel. This can be done several ways:
Remind students to consider what they know about parallel lines. If the lines are
parallel, and one of the other sides acts as a transversal, students can identify angles
that should be congruent.
Remind them that angles 1 and 3 are congruent (since alternate interior angles are
congruent), and angles 1 and 2 are supplementary (since the two angles form a linear
pair), therefore angles 2 and 3 should be supplementary, if the lines are parallel.
If your students are not familar with the properties of parallel lines, they may prove
that the lines are parallel by calculating the slope of the lines they suspect are
Information button contains the coordinates of each vertex. Students may use these coordinates to
find the slope of the appropriate lines.
Allow students to work on their own and to complete the worksheet, should you choose to
provide it. Monitor the room for questions and to be sure that the students are on the correct
Another option: Let students form several groups. Each group should design a different
quadrilateral and prove that its creation fits the desired characteristics of the specified
quadrilateral. The groups could then show the class what they created and how they showed that
the desired characteristics were present.
You may wish to bring the class back together for a discussion of the findings. Once the students
have been allowed to share what they found, summarize the results of the lesson. Especially
emphasize the importance of knowing the characteristics of the different types of quadrilaterals.
Groups of students may take turns creating a quadrilateral and proving that it has the
characteristics necessary to define that shape.
Assign each group a different quadrilateral. Let the groups take turns using the computer to
create the quadrilateral and take note of the information.
When each group has finished, allow the groups an opportunity to teach the class what they
found and how they proved that the necessary characteristics were present.
The class may work together as a whole to create the quadrilaterals suggested on the worksheet.
Students may direct the instructor's movements and suggest calculations that need to be done
before the class.
OR Students may take turns using the demonstration computer to modify the quadrilateral. The
whole class can make the necessary calculations and then check them with a partner.