Difference between revisions of "Functional equation"
Etmetalakret (talk | contribs) |
Tigerzhang (talk | contribs) (→Intermediate Topics) |
||
Line 36: | Line 36: | ||
* [[2006_AMC_12A_Problems/Problem_18 | 2006 AMC 12A Problem 18]] | * [[2006_AMC_12A_Problems/Problem_18 | 2006 AMC 12A Problem 18]] | ||
* [[2007_AIME_II_Problems/Problem_14 | 2007 AIME II Problem 14]] | * [[2007_AIME_II_Problems/Problem_14 | 2007 AIME II Problem 14]] | ||
+ | |||
+ | ==Advanced Topics== | ||
+ | |||
+ | ===Injectivity and Surjectivity=== | ||
==See Also== | ==See Also== |
Revision as of 14:40, 24 August 2021
A functional equation, roughly speaking, is an equation in which some of the unknowns to be solved for are functions. For example, the following are functional equations:
Contents
Introductory Topics
The Inverse of a Function
The inverse of a function is a function that "undoes" a function. For an example, consider the function: . The function
has the property that
. In this case,
is called the (right) inverse function. (Similarly, a function
so that
is called the left inverse function. Typically the right and left inverses coincide on a suitable domain, and in this case we simply call the right and left inverse function the inverse function.) Often the inverse of a function
is denoted by
.
Intermediate Topics
Cyclic Functions
A cyclic function is a function that has the property that:
A classic example of such a function is because
. Cyclic functions can significantly help in solving functional identities. Consider this problem:
Find such that
. In this functional equation, let
and let
. This yields two new equations:
Now, if we multiply the first equation by 3 and the second equation by 4, and add the two equations, we have:
So, clearly,