k
Notes Over 4.5Writing a Direct Variation EquationWriting a Direct Variation Equation
In Exercises 1-6, the variable x and y vary directly. Use the given values to write an equation that relates x and y.
y kx
k
15 5
Direct Variation
Two quantities that model the equation y = kx, where k is the constant of variation
x x
y
x
1 3 15. , x y
3
y 5x
k
Notes Over 4.5Writing a Direct Variation EquationWriting a Direct Variation Equation
In Exercises 1-6, the variable x and y vary directly. Use the given values to write an equation that relates x and y.
y kx
k
3 1
2
Direct Variation
Two quantities that model the equation y = kx, where k is the constant of variation
x x
y
x
2 6 3. , x y
6
y 1
2x
k
Notes Over 4.5Writing a Direct Variation EquationWriting a Direct Variation Equation
In Exercises 1-6, the variable x and y vary directly. Use the given values to write an equation that relates x and y.
y kx
k
4 1
Direct Variation
Two quantities that model the equation y = kx, where k is the constant of variation
x x
y
x
3 4 4. , x y
4
y x
k
Notes Over 4.5Writing a Direct Variation EquationWriting a Direct Variation Equation
In Exercises 1-6, the variable x and y vary directly. Use the given values to write an equation that relates x and y.
y kx
k
2 1
5
Direct Variation
Two quantities that model the equation y = kx, where k is the constant of variation
x x
y
x
4 10 2. , x y
10
y 1
5x
k
Notes Over 4.5Writing a Direct Variation EquationWriting a Direct Variation Equation
In Exercises 1-6, the variable x and y vary directly. Use the given values to write an equation that relates x and y.
y kx
k
7 2
Direct Variation
Two quantities that model the equation y = kx, where k is the constant of variation
x x
y
x
5 35 7. . , x y
35.
y 2x
k
Notes Over 4.5Writing a Direct Variation EquationWriting a Direct Variation Equation
In Exercises 1-6, the variable x and y vary directly. Use the given values to write an equation that relates x and y.
y kx
k
4 1
3
Direct Variation
Two quantities that model the equation y = kx, where k is the constant of variation
x x
y
x
6 12 4. , x y
12
y 1
3x
Notes Over 4.5Using a Ratio to Write a ModelUsing a Ratio to Write a Model
E M150
57120
150
57
5M
The person’s weight on Mars would be pounds. 45
3
5
7. Use the ratio model to estimate a
person’s weight on Mars if the person weighs 120
pounds on Earth.
E M150
57
150
57
228
5
4
Notes Over 4.5Using a Ratio to Write a ModelUsing a Ratio to Write a Model
E M150
5762
9300
57The person’s weight on Earth would
be 163.2 pounds.
8. Use the ratio model to estimate a
person’s weight on Earth if the person weighs 62
pounds on Mars.
E M150
57
E
Notes Over 4.5Using a Ratio to Write a ModelUsing a Ratio to Write a Model
E V160
139
9. A person who weighs 160 pounds on Earth weighs 139 pounds on Venus.
a. Write a model that relates a person’s weight E on Earth to that person’s weight V on Venus.
E kV
k
V V
E
V160139
Notes Over 4.5Using a Ratio to Write a ModelUsing a Ratio to Write a Model
E V160
139
9. A person who weighs 160 pounds on Earth weighs 139 pounds on Venus.
b. A person weighs 195 pounds on Earth. Use the model to estimate that person’s weight on Venus.
160
139 160
139195
32
39
V5421
32The person’s weight on Venus would be
169.4 pounds.