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Translating graphs of functions

The following examples all use this graph as the given \(y = f(x)\):

fx graph

Reflection in the x-axis gives \(y = -f(x)\)

This has the effect of making the y‑coordinate the negative of whatever it was.

reflection x-axis rule
Example
-f(x) graph coordinates for -f(x)
general -f(x)

Note that the x‑coordinate is untouched.

Reflection in the y-axis gives \(y = f(-x)\)

This has the effect of making the x‑coordinate the negative of whatever it was.

reflection y-axis rule
Example
f(-x) graph coordinates for f(-x)
general f(-x)

Note that the y‑coordinate is untouched.

Translate in the x direction to get \(y = f(x \pm c)\)

This shifts the entire graph horizontally left or right.

horizontal translation rule

Remember to go the opposite way to the sign:
For \((x - c)\), go right \(c\) spaces.

x-c translation

For \((x + c)\), go left \(c\) spaces.

x+c translation

Note that the y‑coordinate is untouched.

Example
x+c example x+2 coordinates
Example
x-2 example x-2 coordinates

Translate in the y direction to get \(y = f(x) \pm d\)

This shifts the entire graph vertically up or down.

vertical translation rule

If \(y = f(x) + d\), go up \(d\) spaces:

up translation

If \(y = f(x) - d\), go down \(d\) spaces:

down translation

Note that the x‑coordinate is untouched.

Example
vertical shift example vertical shift coordinates

Scale in the x direction to get \(y = f(bx)\) or \(y = f(x/b)\)

This squashes the graph horizontally when \(b > 1\) and stretches it horizontally when \(b \lt 1\).

horizontal scaling rule

If \(y = f(bx)\), divide the x‑coordinate by \(b\):

divide x by b

If \(y = f(x/b)\), multiply the x‑coordinate by \(b\):

multiply x by b

Note that the y‑coordinate is untouched.

Example
scale x example scale x coordinates
Example
scale x example 2 scale x coordinates 2

Scale in the y direction to get \(y = a f(x)\) or \(y = f(x)/a\)

This stretches the graph vertically when \(a > 1\) and squashes it vertically when \(a \lt 1\).

vertical scaling rule

If \(y = a f(x)\), multiply the y‑coordinate by \(a\):

multiply y by a

If \(y = f(x)/a\), divide the y‑coordinate by \(a\):

divide y by a

Note that the x‑coordinate is untouched.

Example
scale y example scale y coordinates
Example
scale y example 2 scale y coordinates 2

Putting it all together

combined transformations general transformation formula

Apply in order: \(c\), \(b\), \(a\), and finally \(d\).

  1. Shift horizontally C units
  2. Squeeze horizontally b units
  3. Stretch vertically a units
  4. Translate vertically d units
Example

Given \(y = f(x)\) as above, draw the graph \(y = 3f(2x - 2) + 4\).

Comparing the graph with the general form:

general form

Order of translations

  1. \(c = -2\), so shift graph right 2 units
  2. \(b = 2\), so divide x‑coordinates by 2
  3. \(a = 3\), so multiply y‑coordinates by 3
  4. \(d = 4\), so shift the whole graph up 4 spaces

Taking point \((0, -4)\):

rt1

Point \((1, 0)\):

rt2

Point \((3, -4)\):

rt3 complete transformation

Working backwards

Given a translated function:

general transform

Work backwards to get the original \(y = f(x)\).

Instead of applying in order \(c, b, a, d\), apply in order \(d, a, b, c\) — but backwards.

  1. Translate vertically \(d\) units
  2. Stretch vertically \(a\) units
  3. Squeeze horizontally \(b\) units
  4. Shift horizontally \(c\) units
Example

The points \((0, -3)\) and \((1, 6)\) lie on the graph with equation \(y = \tfrac12 f(3x + 2) - 2\).

Find their corresponding original coordinates on the graph \(y = f(x)\).

backwards example bc1

Point \((0, -3)\):

back22

Point \((1, 6)\):

back33

The original point \((5, 16)\) has been translated to \((1, 6)\). The original point \((2, -2)\) has been translated to \((0, -3)\).

Reflect in the line \(y = x\) to get the inverse

…if it exists.

Note that the values of the x and y coordinates are swapped, since the reflection line is \(y = x\).

Example
inverse reflection

Keep it all positive

\(y = |f(x)|\)

The entire graph is above the x‑axis.

Example
modulus graph
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