Vertical Shift of a Function

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What is a Vertical Shift of a Function?

Vertical shift of a function refers to the graph of a function moving up or down the y-axis:

The graph above shows the graph of f(x) = x shifted up three units (from y = 0 to y =3 ) on the vertical (y) axis. The new graph (blue) is now f(x) = x + 3— the original graph plus the 3 unit shift. This leads to a simple rule for any function:

1. Compared to the graph of f(x), a graph f(x) + k is shifted up k units.

We can also work this in reverse:

2. Compared to the graph of f(x), a graph f(x) – k is shifted down k units.

Generally speaking, a vertical shift adds (or subtracts) a constant to (from) each y-value while leaving the x-value unchanged. In other words, the only changes going on here are y-values moving up or down. The x-values stay exactly where they are.

Vertical Shift of a Function: Examples

Example question #1: How are the graphs of f(x) = |x + 2| and f(x) = |x| related?

Solution:
Step 1: Compare the right hand side of the equations:

• |x + 2|
• |x|.

The difference between these two statements is the “+ 2”.

Step 2: Choose one of the above statements based on the result from Step 1. We have a positive 2, so choose statement 1:
Compared to the graph of f(x), a graph f(x) + k is shifted up k units.

Step 3: Replace the f(x) and f(x) + k the statement with your functions.
Compared to the graph of f(x) = |x|, a graph f(x) = |x + 3| is shifted up k units.

Example question #2: How are the graphs of f(x) = 3x² and f(x) = 3x² – 8 related?

Solution:
Step 1: Compare the right hand side of the equations:

• 3x²
• 3x² – 8

The difference between these two statements is the “- 8”.

Step 2: Choose one of the above statements based on the result from Step 1. We have a negative 8, so choose statement 2:
Compared to the graph of f(x), a graph f(x) + k is shifted down k units.

Step 3: Replace the f(x) and f(x) + k the statement with your functions.
Compared to the graph of f(x) = 3x², a graph f(x) = 3x² – 8 is shifted down k units.

References

Larson, R. & Edwards, B. (2016). Calculus (10th Edition). Cengage Learning.