Section 2.3 Transformations of Graphs
Subsection 1. Interpret function notation for transformations
Horizontal transformations affect the \(x\)-coordinate of a graph, so they are accomplished by a change in the \(x\)-coordinate of the equation, before the function is applied.
Vertical transformations affect the \(y\)-coordinate of a graph, so they are accomplished by a change in the \(y\)-coordinate of the equation, after the function is applied.
Subsubsection Examples
Example 2.28.
Write a formula for the transformed function.
- \(\displaystyle f(x)=\dfrac{1}{x},~~g(x)=f(x)-3\)
- \(\displaystyle f(x)=\dfrac{1}{x^2},~~g(x+4)\)
- \(\displaystyle f(x)=\sqrt[3]{x},~~g(x)=\dfrac{1}{3}f(x)\)
- \(\displaystyle f(x)=|x|,~~g(x)=-f(x)\)
- We subtract 3 from the formula for \(f(x)\text{:}\) \(~~g(x)=\dfrac{1}{x}-3\)
- We add 4 to \(x\) before applying the function. Think of replacing \(x\) by \(x+4\) wherever it appears in the formula for \(f(x)\text{:}\) \(~~g(x)=\dfrac{1}{(x+4)^2}\)
- We multiply the formula for \(f(x)\) by \(\dfrac{1}{3}\text{:}\) \(~~g(x)=\dfrac{1}{3}\sqrt[3]{x}\)
- We make the formula for \(f(x)\) negative: \(~~g(x)=-|x|\)
Example 2.29.
Write a formula for the transformed function.
- \(\displaystyle f(x)=x^2-3x,~~g(x)=f(x+1)\)
- \(\displaystyle f(x)=x^3+\sqrt{x},~~g(x)=-2f(x)\)
- \(\displaystyle f(x)=5-\dfrac{2}{x},~~g(x)=f(x)-8\)
- \(\displaystyle f(x)=\dfrac{4x-7}{x^2},~~g(x)=f(x-2)\)
- We replace \(x\) by \(x+1\) wherever it appears in the formula for \(f(x)\text{:}\) \(~~g(x)=(x+1)^2-3(x+1)\)
- We multiply the formula for \(f(x)\) by \(-2\text{:}\) \(~~g(x)=-2x^3-2\sqrt{x}\)
- We subtract 8 from the formula for \(f(x)\text{:}\) \(~~g(x)=-3-\dfrac{2}{x}\)
- We replace \(x\) by \(x-2\) wherever it appears in the formula for \(f(x)\text{:}\) \(~~g(x) = \dfrac{4(x-2)-7}{(x-2)^2}\)
Subsubsection Exercises
Checkpoint 2.30.
Write formulas for the transformed functions.
- \(\displaystyle g(x)=f(x-3)\)
- \(\displaystyle h(x)=f(x)-3\)
- \(\displaystyle g(x)=(x-3)^2-3(x-3)+5\)
- \(\displaystyle h(x)=x^2-3x+2\)
Checkpoint 2.31.
Write formulas for the transformed functions.
- \(\displaystyle g(x)=f(x)+1\)
- \(\displaystyle h(x)=f(x+1)\)
- \(\displaystyle g(x)=\dfrac{\sqrt{x}}{2x-1}+1\)
- \(\displaystyle h(x)=\dfrac{\sqrt{x+1}}{2(x+1)-1}\)
Checkpoint 2.32.
Write formulas for the transformed functions.
- \(\displaystyle g(x)=f(x)-2\)
- \(\displaystyle h(x)=f(x-2)\)
- \(\displaystyle g(x)=x^3-|x|-2\)
- \(\displaystyle h(x)=(x-2)^3-|x-2|\)
Checkpoint 2.33.
Write formulas for the transformed functions.
- \(\displaystyle g(x)=3f(x)\)
- \(\displaystyle h(x)=\dfrac{-1}{3}f(x)\)
- \(\displaystyle g(x)=\dfrac{3(x-1)}{x^2}\)
- \(\displaystyle h(x)=\dfrac{-(x-1)}{3x^2}\)
Subsection 2. Make a table for a transformed function
Subsubsection Examples
Example 2.34.
Complete the table for the function and its transformation.
\(x\) | \(-2\) | \(-1\) | \(0\) | \(1\) | \(2\) |
\(f(x)\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) |
\(g(x)\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) |
This transformation is a shift in the \(y\)-direction. We subtract 4 from each value of \(f(x)\text{.}\)
\(x\) | \(-2\) | \(-1\) | \(0\) | \(1\) | \(2\) |
\(f(x)\) | \(-8\) | \(-1\) | \(0\) | \(1\) | \(8\) |
\(g(x)\) | \(-12\) | \(-5\) | \(-4\) | \(-3\) | \(4\) |
Example 2.35.
Complete the table for the function and its transformation.
\(x\) | \(-4\) | \(-2\) | \(0\) | \(2\) | \(4\) |
\(f(x)\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) |
\(g(x)\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) |
This transformation is a shift in the \(x\)-direction. It is helpful to insert another row into the table.
\(x\) | \(-4\) | \(-2\) | \(0\) | \(2\) | \(4\) |
\(x-4\) | \(-8\) | \(-6\) | \(-4\) | \(-2\) | \(0\) |
\(f(x-4)\) | \(8\) | \(6\) | \(4\) | \(2\) | \(0\) |
\(g(x)\) | \(8\) | \(6\) | \(4\) | \(2\) | \(0\) |
Subsubsection Exercises
Checkpoint 2.36.
Complete the table for the function and its transformation.
\(x\) | \(-4\) | \(-2\) | \(0\) | \(2\) | \(4\) |
\(f(x)\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) |
\(g(x)\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) |
\(x\) | \(-4\) | \(-2\) | \(0\) | \(2\) | \(4\) |
\(f(x)\) | \(\dfrac{-1}{4}\) | \(\dfrac{-1}{2}\) | undefined | \(\dfrac{1}{2}\) | \(\dfrac{1}{4}\) |
\(g(x)=-2f(x)\) | \(\dfrac{1}{2}\) | \(1\) | undefined | \(-1\) | \(\dfrac{-1}{2}\) |
Checkpoint 2.37.
Complete the table for the function and its transformation.
\(x\) | \(-4\) | \(-2\) | \(0\) | \(2\) | \(4\) |
\(f(x)\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) |
\(g(x)\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) | \(\hphantom{00}\) |
\(x\) | \(-4\) | \(-2\) | \(0\) | \(2\) | \(4\) |
\(x+1\) | \(-3\) | \(-1\) | \(1\) | \(3\) | \(5\) |
\(f(x)\) | \(16\) | \(4\) | \(0\) | \(4\) | \(16\) |
\(g(x)=f(x-1)\) | \(9\) | \(1\) | \(1\) | \(9\) | \(25\) |
Subsection 3. Identify the order of operations in a transformed function
First, identify the basic functions. Then follow the order of operations to describe the transformation.
Subsubsection Examples
Example 2.38.
State the basic function and the transformations needed to graph \(~~F(x)=5 \sqrt[3]{x}+6\text{.}\)
The basic function is \(~f(x)=\sqrt[3]{x}~\text{.}\) The output is multiplied by 5, and then 6 is added, so the transformations are
- \(~g(x)=5f(x)~\text{,}\) so the basic graph is stretched vertically by a factor of 5
- and \(~F(x)=g(x)+6~\text{,}\) so \(g(x)\) is shifted up by 6 units.
Example 2.39.
State the basic function and the transformations needed to graph \(~~G(x)=\dfrac{-3}{(x-1)^2}\text{.}\)
The basic function is \(~f(x)=\dfrac{1}{x^2}~\text{.}\) We subtract 1 from the input, then multiply the output by \(-3\text{,}\) so the transformations are
- \(~g(x)=f(x-1)~\text{,}\) so the basic graph is shifted 1 unit to the right
- and \(~G(x)=-3g(x)~\text{,}\) so \(g(x)\) is reflected about the \(x\)-axis and stretched vertically by a factor of 3.
Subsubsection Exercises
Checkpoint 2.40.
State the basic function and the transformations needed to graph
The basic function is \(~f(x)=\sqrt{x}~\text{.}\) Then
- \(~g(x)=f(x+6)~\text{:}\) shift 6 units left
- \(~F(x)=g(x)+2~\text{:}\) shift 2 units up
Checkpoint 2.41.
State the basic function and the transformations needed to graph
The basic function is \(~f(x)=x^3~\text{.}\) Then
- \(~g(x)=f(x-3)~\text{:}\) shift 3 units right
- \(~F(x)=\dfrac{1}{4}g(x)~\text{:}\) compress vertically by a factor of 4