Transcript MJ3 - Davidsen Middle School

MJ3
Ch 7.1 – Area of Parallelograms,
Triangles & Trapezoids
Bellwork
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Get your bellwork sheet and a pencil and
meet me in front of the media center.
After The Activity
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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
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None
Before we begin…
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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
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Students will calculate the area of
parallelograms, triangles and trapezoids
using the formula method
The Formula Method
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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:
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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
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Calculate Area:
A=l●w
1. Write the Formula
A=4●8
2. Substitute
A = 32 ft2
3. Do the math
4 ft
8 ft
Note: The answer
is squared
because you are
measuring 2
dimensions
(Length & Width)
Parallograms
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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
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Find Area
1. Write the Formula A = bh
2. Substitute
A = 5.25(12)
3. Do the math
A = 63 m2
12 m
5.25 m
Your Turn
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In the notes section of your notebook draw
and label the picture and then calculate area
using the formula method.
25 mm
16.25 ft
5 mm
8 ft
Triangles
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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
Height
A = ½ bh
Base
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You can find this formula on the FCAT reference
sheet
Example
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Calculate Area
4.5 m
8.5 m
1. Write the Formula A = ½ bh
2. Substitute
A = ½ (8.5)(4.5)
3. Do the math
A = ½ (38.25)
A = 19.125 m2
Your Turn
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In the notes section of your notebook draw
and label the figure and then calculate area
using the formula method
10 m
18 m
6 ft
20 m
12 m
10.5 ft
Trapezoids
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Parallel Sides
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
Example
9 mm
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Calculate Area
4.5 mm
6.5 mm
18.5 mm
1. Write the Formula A = ½ h(b1 + b2)
2. Substitute
A = ½ (6.5)(18.5 + 9)
3. Do the math
A = ½ (6.5)(27.5)
A = ½ (178.75)
A = 89.375 mm2
Your Turn
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In the notes section of your notebook draw
and label the figure and then calculate area
using the formula method.
9 cm
3.2 cm
6.5 cm
4 cm
Summary
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In the notes section of your notebook
summarize the key concepts covered in
today’s lesson
Today we discussed
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The difference between perimeter & area
How to calculate area using the formula method
Assignment
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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