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Graphically Represent the Inverse of a Function |
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Definition of Inverse:
If the graph of a function contains a point (a,b),
then the graph of the inverse of the function contains the point (b,a).
To graph the inverse of a function, reverse the ordered pairs of the
original function.
If f is a given
function, then f -1 denotes the inverse of f.
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"The
x- and y- coordinates
switch places!"
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Note:
The inverse of a function MAY NOT be a
function.
If the inverse is also a
function, it is referred to as the
inverse function. |
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Method 1 -
Determine graphically if a
function has an inverse which is also a function:
Use the
horizontal line test
to determine if a function has an inverse function.
If ANY horizontal line intersects your original function in ONLY ONE
location, your function has an inverse which is also a function.
The function y = 3x + 2, shown at the right, HAS
an inverse function because it passes the horizontal line test.
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Method 2 -
Determine graphically if a
function has an inverse which is also a function: If a
function has an inverse function, the
reflection of that original
function in the identity line y = x will
also be a function (it
will pass the vertical line test for functions).
The example at the left shows the original
function, y = x2 , in blue.
The reflection over the identity line y = x is shown in
red. The
red dashed line will not pass the
vertical line test for functions, thus y = x2 does not
have an inverse function.
You can see that the inverse exists,
but it is NOT a function. |
NOTE:
With functions such as y = x2 , it is possible
to restrict the domain to obtain an inverse function for a
portion of the graph.
This means that you will be looking at only a selected section of the
original graph that will pass the horizontal line test for
the existence of an inverse function. For
example:
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or
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by restricting the graph in such a manner, you
guarantee the existence of an inverse function for a portion of the
graph.
(Other restrictions are also possible.) |
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