Lesson 3-7 Pages 131-136
Using Formulas
What you will learn!1. How to solve problems by using formulas.
2. How to solve problems involving the perimeters and areas of rectangles.
FormulaFormulaPerimeterPerimeterAreaArea
What you really need to know!
Formulas are sets of instructions that need to be followed.
Write the formula.
Replace the variables.
Solve.
Example 1:
If you travel 135 miles in 3 hours, what is your average speed in miles per hour?
d = rt
135 = r(3)
45 = r
45 mph
Example 2:
Find the perimeter of the rectangle.
70 cm15
cm
20 cm
p = 2l + 2w
p = 2•20 + 2•15
Example 3:
The perimeter of a rectangle is 60 feet. Its width is 9 feet. Find its length.
p = 2l + 2w60 = 2l + 2•960 = 2l + 18
Example 3:
The perimeter of a rectangle is 60 feet. Its width is 9 feet. Find its length.
42 = 2l21 = l
21 feet
60 = 2l + 18
a = lw
a = 14•6
a = 84 ft2
Example 4:
Find the area of a rectangle with length 14 feet and width 6 feet.
84 ft26
ft
14 ft Area Demo
Example 5:
The area of a rectangle is 40 square meters. Its length is 8 meters. Find its width.
a = lw40 = 8w5 = w
5 m
Page 133
Guided Practice
#’s 4-9
Pages 131-133 with someone at home and study
examples!
Read:
Homework: Pages 134-136
#’s 10-32 even,
33-34, 38, 40
#’s 44-53Lesson Check CH-3
Page
730
Lesson 3-7
Lesson Check CH-3
Study Guide and Review
Pages
138-140
#’s 1-38(Odd answers in back of book)
Prepare for Test!
Page
141
#’s 1-25
Prepare for Test!
Pages
142-143
#’s 1-19
