Area of Parallelograms and Trapezoids

Day 3

Objectives:

To derive formulas for the area of a parallelogram and a trapezoid.

To apply area formulas to solve problems.

Warm Up Activity:

Diamond Dazzler

First count all the diamond shapes in this design.

(20)

Then count all the triangles.

(17)

Lesson Outline:

The class will divide into three groups. The third group will consist of the students who have already mastered the unit and should be assigned the optional activity.
The two groups of students who have not mastered the objectives will derive the areas of parallelograms and trapezoids based on their knowledge of the are of triangles and rectangles. Each group will be given an overhead to show their discoveries.
- Click here for GSP sketches that might help.
The groups will present in the following order:
- areas of parallelograms
- areas of trapezoids
- unknown height (today's optional activity)
- other ways to find the area of a triangle (day 2's optional activity)
At the close of class the exact formulas for the area of parallelograms, trapezoids, triangles, and rectangles will be reviewed.

Optional Activity :

This is the third group which is made up of students who have already mastered today's objectives determined by the pre-test. This group will answer the question of what if you don't know the height of a parallelogram or trapezoid. They will also prepare an overhead for demonstration for the class.