Warm Up

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Preview
Warm Up
California Standards
Lesson Presentation
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Warm Up Find each product. 1. 8 ? 12 2. 3 3.
9.4 ? 6.3 4. 3.5 ? 7
96
1 3
1 2
? 5
59.22
24.5
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AF3.1 Use variables in expressions describing
geometric quantities (e.g., P 2w 2l, A
bh, C pdthe formulas for the perimeter of a
rectangle, the area of a triangle, and the
circumference of a circle, respectively). Also
covered NS2.1, AF1.1, AF2.1, AF3.2
1 2
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Vocabulary
area base height
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The area of a figure is the number of
non-overlapping unit squares needed to cover the
figure. Area is measured in square units.
Area 15 square units
The base of a parallelogram is the length of one
side. Its height is the perpendicular distance
from the base to the opposite side.
For a rectangle, the base is the same as the
length, and the height is the same as the width.
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Additional Example 1 Finding the Area of a
Parallelogram
Find the area of the parallelogram.
A bh
Use the formula.



A 16
8
Substitute for b and h.
8 m

Multiply.
A 128
16 m
The area of the parallelogram is 128 m2.
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Additional Example 2 Finding the Area of a
Rectangle
Find the area of the rectangle.
4.5 in.
7.4 in.
A lw
Use the formula.
A 7.4 4.5
Substitute for l and w.
Multiply.
A 33.3
The area of the rectangle is 33.3 in2.
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Additional Example 3 Finding Length or Width of
a Rectangle
The area of a playing field is 1,470 ft2 and the
length is 42 ft. What is the width of the field?
Use the formula for the area of a rectangle.
A lw
1,470 42 w
Substitute 1,470 for A and 42 for l.
1,470 42
42 w 42

Divide both sides by 42 to isolate w.
35 w
The width of the playing field is 35 ft.
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Additional Example 4 Measurement Application
A carpenter is laying a wood floor measuring 4 yd
by 5 yd. How many square feet of flooring
material does she need?
Step 1 Draw and label a diagram.
Step 2 Convert the units.
The wood floor is measured is yards, but the
answer should be in feet.
3 ft 1 yd
4 yd 12 ft
Convert yards to feet by multiplying by a ratio
equal to 1.
3 ft 1 yd
5 yd 15 ft
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Additional Example 4 Continued
A carpenter is laying a wood floor measuring 4
yd by 5 yd. How many square feet of flooring
material does she need?
Step 3 Find the area of the floor in square feet.
A lw
Use the formula for the area of a rectangle.
A 12 15
Substitute 12 for l and 15 for w.
A 180
Multiply.
The carpenter needs 180 ft2 of flooring material.
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Check It Out! Example 1
Find the area of the parallelogram.
A bh
Use the formula.



A 12
6
Substitute for b and h.
6 cm
Multiply.
A 72
12 cm
The area of the parallelogram is 72 cm2.
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Check It Out! Example 2
Find the area of the rectangle.
6.3 in.
8.2 in.
A lw
Use the formula.
A 8.2 6.3
Substitute for l and w.
Multiply.
A 51.66
The area of the rectangle is 51.66 in2.
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Check It Out! Example 3
The area of a rectangular parking lot is 3,570
ft2 and the width is 70 ft. What is the length of
the parking lot?
Use the formula for the area of a rectangle.
A lw
3,570 l 70
Substitute 3,570 for A and 70 for w.
3,570 70
l 70 70

Divide both sides by 70 to isolate l.
51 l
The length of the parking lot is 51 ft.
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Check It Out! Example 4
A carpenter is laying a tile floor measuring 5 yd
by 7 yd. How many square feet of tile material
does she need?
5 yd
Step 1 Draw and label a diagram.
7 yd
Step 2 Convert the units.
The tile floor is measured is yards, but the
answer should be in feet.
3 ft 1 yd
5 yd 15 ft
Convert yards to feet by multiplying by a ratio
equal to 1.
3 ft 1 yd
7 yd 21 ft
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Check It Out! Example 4 Continued
A carpenter is laying a tile floor measuring 5 yd
by 7 yd. How many square feet of tile material
does she need?
Step 3 Find the area of the tile floor in square
feet.
A lw
Use the formula for the area of a rectangle.
A 15 21
Substitute 15 for l and 21 for w.
A 315
Multiply.
The carpenter needs 315 ft2 of tile material.
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Lesson Quiz Part I
Find the area of each figure. 1.
2. 3.
24.5 ft2
4.
84 ft2
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Lesson Quiz Part II
5. Diego is building a rectangular platform
measuring 36 in. by 54 in. What is the area of
the platform in square feet?
13.5 ft2