MJ3

Ch 7.1 – Area of Parallelograms, Triangles & Trapezoids

Bellwork

Get your bellwork sheet and a pencil and meet me in front of the media center.

After The Activity

Raise you hand if you can predict why I had you do this activity…

What is perimeter? What is Area? From a rectangle we can create a

parallelogram…(demonstrate w/index card)

My comments….

Assignment Review

None

Before we begin…

Please take out your notebook and get ready to work… In the bellwork activity we looked at the perimeter of a

square… At this stage you should all know the difference

between perimeter and area… More specifically, you should know by rote memory how

to calculate the area of a square or rectangle… In today’s lesson we will look at how to calculate the

area of parallelograms, triangles and trapezoids…

Objective 7.1

Students will calculate the area of parallelograms, triangles and trapezoids using the formula method

The Formula Method First and foremost…in this chapter the only way that I will

accept any answers is if you use the formula method! At this level you are required to demonstrate what you

know and the formula method helps you do that. The formula method is:

Write the formula Substitute

Do the math

Note: Each time you perform a function you must rewrite the whole equation all over again…this strategy minimizes

errors!

Example Calculate Area:

4 ft

8 ft

1. Write the Formula

2. Substitute

3. Do the math

A = l ● w

A = 4 ● 8

A = 32 ft2

Note: The answer is squared because you are measuring 2 dimensions (Length & Width)

Parallograms Let’s look at the specific characteristics of a

parallelogram… In a parallelogram the base can be any side. The height (altitude) is a line segment that is

perpendicular to the base and runs to the opposite side.

The formula for area of a parallelogram is:A = bh

The formula can be found on the FCAT reference sheet

Example

Find Area

12 m

5.25 m

A = bh

A = 5.25(12)

A = 63 m2

1. Write the Formula

2. Substitute

3. Do the math

Your Turn

In the notes section of your notebook draw and label the picture and then calculate area using the formula method.

5 mm

25 mm

8 ft

16.25 ft

Triangles A diagonal drawn in a Parallograms will separate

the parallelogram into 2 congruent triangles Therefore, the area of a triangle

will be ½ of the area of a parallelogram

The base can be any side and the height (altitude) is the line segment from the base to the opposite side.

The formula for area of a triangle is A = ½ bh

You can find this formula on the FCAT reference sheet

Height

Base

Example

Calculate Area

4.5 m

8.5 m

A = ½ bh

A = ½ (8.5)(4.5)

A = ½ (38.25)

A = 19.125 m2

1. Write the Formula

2. Substitute

3. Do the math

Your Turn

In the notes section of your notebook draw and label the figure and then calculate area using the formula method

6 ft

10 m

10.5 ft12 m

18 m20 m

Trapezoids

In chapter 6 we discussed

trapezoids, which are

quadrilaterals with 2 parallel sides. The parallel sides are the bases. It doesn’t

matter which one you call b1 or b2

The formula for area of trapezoids is

A = ½ h(b1 + b2) This formula can also be found on the FCAT

reference sheet

Parallel Sides

Example

Calculate Area6.5 mm

18.5 mm

9 mm

4.5 mm

A = ½ h(b1 + b2)

A = ½ (6.5)(18.5 + 9)

A = ½ (6.5)(27.5)

A = ½ (178.75)

A = 89.375 mm2

1. Write the Formula

2. Substitute

3. Do the math

Your Turn

In the notes section of your notebook draw and label the figure and then calculate area using the formula method.

3.2 cm

6.5 cm

9 cm

4 cm

Summary

In the notes section of your notebook summarize the key concepts covered in today’s lesson

Today we discussed The difference between perimeter & area How to calculate area using the formula method

Assignment

Text p. 317 # 7 – 15 You do not have to draw the figure. However, you must use the formula method

to show how you got your answer. (no work = no credit)

This assignment is due tomorrow I do not accept late assignments