1. Transforming Linear Equations

2. Linear Equations
Family of functions – a set of functions whose graphs have basic characteristics in common. For example, all linear functions form a family because all of their graphs are the same (they are lines).
Parent Function – the most basic function in a family. For linear functions, the parent function is f(x)= x.

3. Linear Equations
Transformation – A change in position or size of a figure.
Three types of transformations
Translation (slide)
Rotation (turn)
Reflection (flip)

4. Translations
When we “slide” the parent function f(x) = x, it will move the function up or down on the y-axis or left or right on the x-axis.
This changes the y-intercept (b).
The slopes (m) will stay the same.

5. Notice all the lines on this graph are parallel.
The slopes are the same but the y-intercepts
are different.

6. The graphs of g(x) = x + 3, h(x) = x – 2, and
k(x) = x – 4, are vertical translations of the graph of the parent function, f(x) = x. A translation is a type of transformation that moves every point the same distance in the same direction. You can think of a translation as a “slide.”

7. Reflections
When we reflect (flip) a transformation across a line it produces a mirror image across the y-axis.
When the slope (m) is multiplied by -1 the graph is reflected across the y-axis.
It is possible to reflect a line over the x-axis as well. More about that later.

8. The diagram shows the reflection of the graph of f(x) = 2x across the y-axis, producing the graph of g(x) = –2x. A reflection is a transformation across a line that produces a mirror image. You can think of a reflection as a “flip” over a line.

9. To find g(x), multiply the value of m by –1. In f(x) = x + 2, m = .
Graph f(x) = (2/3)x + 2. Then reflect the graph of f(x) across the y-axis. Write a function g(x) to describe the new graph.
g(x)
f(x)
To find g(x), multiply the value of m by –1.
In f(x) = x + 2, m = .
g(x) = – x + 2

10. Rotation Rotation – a transformation about a point.
You can think of a rotation as a “turn”.
The y-intercepts are the same, but the slopes are different.
When the slope is changed it will cause a rotation about the point that is the y-intercept changing the line’s steepness or slope.

11. The graphs of g(x) = 3x, h(x) = 5x, and k(x) = are rotations of the graph f(x) = x. A rotation is a transformation about a point. You can think of a rotation as a “turn.” The y-intercepts are the same, but the slopes are different.

12. What change in the parent function causes…
A translation?
A rotation?
A reflection?
Changing the y-intercept (b),
slope is the same
Changing the slope, y-intercept
stays the same
Multiplying the slope by -1,
y-intercept stays the same

13. Find transformations of f(x) = x that will result in g(x) = 2x – 3:
Graph f(x) = x and g(x) = 2x – 3. Then describe the transformations from the graph of f(x) to the graph of g(x).
Find transformations of f(x) = x that will result in g(x) = 2x – 3:
h(x) = 2x
Multiply f(x) by 2 to get h(x) = 2x. This rotates the graph about (0, 0) and makes it parallel to g(x).
f(x) = x
Then subtract 3 from h(x) to get g(x) = 2x – 3. This translates the graph 3 units down.
g(x) = 2x – 3
The transformations are a rotation and a translation.

14. If the charge per flower is lowered to $3.00?
A florist charges $25 for a vase plus $4.50 for each flower. The total charge for the vase and flowers is given by the function f(x) = 4.50x How will the graph change if the vase’s cost is raised to $35?
If the charge per flower is lowered to $3.00?
Total Cost
f(x) = 4.50x + 25 is graphed in blue.
If the vase’s price is raised to $35, the new function is
f(g) = 4.50x The original graph will be translated 10 units up.

15. (0, 25) and become less steep.
A florist charges $25 for a vase plus $4.50 for each flower. The total charge for the vase and flowers is given by the function f(x) = 4.50x How will the graph change if the vase’s cost is raised to $35? If the charge per flower is lowered to $3.00?
Total Cost
If the charge per flower is lowered to $3.00. The new function is h(x) = 3.00x The original graph will be rotated clockwise about
(0, 25) and become less steep.

16. Try these…
Describe the transformation from the graph of f(x) to the graph of g(x).
1. f(x) = 4x, g(x) = x 2. 3. 4.
rotation (1/4 of the original steepness)
f(x) = x – 1, g(x) = x + 6
translated 7 units up
f(x) = x, g(x) = 2x
Rotation (10 times steeper)
f(x) = 5x, g(x) = –5x
Reflection

17. Try these… Part II
5. f(x) = x, g(x) = x – 4 6.
translation 4 units down
f(x) = –3x, g(x) = –x + 1
rotation (1/3 of the original steepness), translation 1 unit up
7. A cashier gets a $50 bonus for working on a holiday plus $9/h. The total holiday salary is given by the function f(x) = 9x How will the graph change if the bonus is raised to $75? if the hourly rate is raised to $12/h?
translation 25 units up; rotated (4/3 times the original steepness)