January 03, 2015
Lesson 4.3: Area of a Parallelogram
OBJECTIVE: Develop and apply a formula for determining the area of:
• triangles, parallelograms and, circles.
Get Started:
Look at the shapes at the top of page 139.
Which of the shapes are
parallelograms?
How would you describe a parallelogram?
How are shapes C and D alike?
How are shapes C and D different?
Why is shape B not a parallelogram?
January 03, 2015
p. 139 Explore:
Step 1:
Copy Parallelogram A on grid paper. Estimate, then find the area of
the parallelogram. (Describe to me your strategy!)
Step 2:
Cut out the parallelogram. Then, cut along the broken line segment.
Step 3:
Arrange the two pieces to form a rectangle.
What is the area of the rectangle? (How did you find this?)
How does the area of the rectangle compare to the area of the
parallelogram?
January 03, 2015
p. 139 Explore cont.:
Step 1:
Copy Parallelogram B on grid paper. Estimate, then find the area of
the parallelogram.
Step 2:
Cut out the parallelogram. Then, cut along the broken line segment.
Step 3:
Arrange the two pieces to form a rectangle.
What is the area of the rectangle?
How does the area of the rectangle compare to the area of the
parallelogram?
p. 139 Explore cont.:
Step 1:
Copy Parallelogram C on grid paper. Estimate, then find the area of
the parallelogram.
Step 2:
Cut out the parallelogram. Then, cut along the broken line segment.
Step 3:
Arrange the two pieces to form a rectangle.
What is the area of the rectangle?
How does the area of the rectangle compare to the area of the
parallelogram?
January 03, 2015
p. 140 Connect:
Let's share our results with the class...
Show me how you cut one of the parallelograms to create a rectangle.
Things to ponder...
Can every parallelogram be changed into a rectangle by cutting and moving one piece?
Can you write a rule (formula) for finding the area of a parallelogram?
Examples:
Calculate the area of each parallelogram...
1.
7 cm
5 cm
2.5 m
2.
7.5 m
January 03, 2015
3. Calculate the base of the parallelogram
A = 40cm2
h = 8cm
b = ? cm
4. Calculate the height of the parallelogram
2
A = 150m
h=?m
b = 20 m
Homework:
p. 141 #1a, 2, 6, 7a, 8, & 9 (AFQ)