1. Measurement of 2D Figures
Math Alliance
April 5, 2011
Measurement of 2D Figures

2. Process of Measurement
Decide on the attribute to be measured
Select a unit that has that attribute
Fill, cover or match the unit to the attribute of the object

3. Investigation
“If the unit of area is a regular sheet of typing paper, about what is the area of one side of a typical door?”
Individually, develop a conjecture.
As a table, discuss your conjectures.

4. Big Ideas for Measuring Area
Area is defined by covering.
(The Moving Principle) The area of a shape does not depend on its position or orientation.  
(The Combining Principle) Area is additive.

5. Area of Parallelograms & Triangles
Area of a Triangle =
Length x width /2
Area of a Parallelogram =
Length x width

6. Area of Polygons
The Johnsons own a lot that has a creek running behind it. How could they find the area of the lot?

7. How about this? a s

8. Or this? s a

9. Or This?

10. From Polygons to Circles
Area = ½ (a)(p)
Area = ?
How do we get from here…
…to here?

11. “Everyday” Circles Take measurements of your circles
Which measurements did you use?
What relationships did you see?

12. “Everyday” Circles
How we can we use these measurements to find the area of a circle?

13. Homework Read Sections 12.1 & 12.2
Turn in: 71, 80,
Section 12.2: 2-6, 11, 14, 15, 18, 20, 23, 35, 36, 37, 44, 57, 58, 67, 69
Turn in: 2-6, 23, 36, 57, 58, 67
Triangle Problem: “You are given 1200 m of fencing. You need to create a triangular garden. What is the largest garden you can make with this fencing?”