Question 1161665
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You may take, for example, g(x) = ax + b any linear function with a =/= 0,


and take f(x) = g(x) as the same function.


Then you will have the desired identity.



More generally, you can take g(x) as any monotonic one-to-one function   g: R ---> R   defined over all real numbers;

for example,   g(x) = x^3;   or    g(x) = x^5;   or    g(x) = x^7,    and so on . . . 


and take   f(x) = g(x).


Then,  again,  you will have the desired identity.