Big Ideas Math Algebra 2, 2014
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Big Ideas Math Algebra 2, 2014 View details
7. Transformations of Polynomial Functions
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Exercise 18 Page 209

Consider vertical and horizontal translations, stretches and shrinks, and reflections.

Rule for g: g(x)=3x^5-6x+9
Transformation: Vertical stretch by a factor of 3.
Graph:

Practice makes perfect

We will describe the graph of g as a transformation of the graph of f. Then we will write a rule for g. Finally, we will graph the functions.

Describing the Transformation

To describe and graph the given transformation, g(x)=3f(x), let's look at the possible transformations. Then we can more clearly identify the ones being applied to the function f(x)=x^5-2x+3.

Vertical Stretch or Shrink
Vertical stretch, a>1 y= af(x) Vertical shrink, 0< a< 1 y= af(x)
Now, using the table, let's highlight the transformations of f(x).

g(x)= 3f(x) We can describe the transformation as a vertical stretch by a factor of 3.

Finding the Rule for g(x)

To obtain the rule for g(x), we will write the rule for 3f(x). To do so, we will multiply the formula of f(x) by 3. f(x)=x^5-2x+3 ⇒ 3f(x)= 3(x^5-2x+3) Let's now simplify the above formula.
3f(x)=3(x^5-2x+3)
3f(x)=3x^5+3 * (- 2x)+3 * 3
3f(x)=3x^5-6x+9
Therefore, as g(x)=3f(x), we got that g(x)=3x^5-6x+9.

Graphing the Functions

Let's make a table of values for both functions.

Input f(x) g(x)
x x^5-2x+3 f(x)=x^5-2x+3 3x^5- 6x+9 g(x)=3x^5-6x+9
- 1.5 ( - 1.5)^5-2( - 1.5)+3 - 1.59375 3( - 1.5)^5-6( - 1.5)+9 - 4.78125
- 1 ( - 1)^5-2( - 1)+3 4 3( - 1)^5-6( - 1)+9 12
0 0^5-2 * 0+3 3 3 * 0^5-6 * 0+9 9
1 1^5-2 * 1+3 2 3 * 1^5-6 * 1+9 6
1.5 1.5^5-2 * 1.5+3 7.59375 3 * 1.5^5-6 * 1.5+9 22.78125

Finally, we plot the points of each function and connect them with smooth curves.