The graph of a function can be moved up, down, left, or right by adding to or
subtracting from the output or the input.
Adding to the output of a function moves the graph up.
Subtracting from the output of a function moves the graph down.
Here are the graphs of y = f (x), y = f (x) + 2, and y = f (x) - 2. Note
that if (x, y1) is a point on the graph of f (x), (x, y2) is a point on
the graph of f (x) + 2, and (x, y3) is a point on the graph of f (x) - 2,
then y2 = y1 + 2 and y3 = y1 - 2. For example, (1, 2) is on the graph
of f (x), (1, 4) is on the graph of f (x) + 2, and (1, 0) is on the graph
of f (x) - 2.
Graphs of f (x), f (x) + 2, and f (x) - 2
While adding to the input increases the function in the y direction, adding to
the input decreases the function in the x direction. This is because
the function must compensate for the added input. If the function outputs "7"
when "3" is input, and we input x + 2, the function will output "7" when
x = 1.
Thus, adding to the input of a function moves the graph left, and
subtracting from the input of a function moves the graph right.
Here are the graphs of y = f (x), y = f (x + 2), and y = f (x - 2). Note
that if (x1, y) is a point on the graph of f (x), (x2, y) is a point on
the graph of f (x + 2), and (x3, y) is a point on the graph of f (x - 2),
then x2 = x1 - 2 and x3 = x1 + 2. For example, (1, - 2) is on the
graph of f (x), (- 1, - 2) is on the graph of f (x + 2), and (3, - 2) is on
the graph of f (x - 2).
Graphs of f (x), f (x + 2), and f (x - 2)
A shift of the graph up, down, left, or right, without changing the shape, size,
or dimensions of the graph, is called a translation.
Examples: If f (x) = x2 + 2x, what is the equation if the graph is
shifted:
a) 4 units up
b) 4 units down
c) 4 units left
d) 4 units right
