Finding $f(x)$ from a functional equation
13042
Finding a function from the given functional equation .
133333
Find $f(x)$ for $f(f(x))=\sin x$
111556
Solving functional equation $f(x+y)+f(x-y)=2f(x)\cos y$?
42699
Solve for $f(x)$ if $f(f(x))=6x-f(x)$
111789
Solving functional differential equation $f'(x)=2f(2x)-f(x)$
67594
Books on functional equations
111756
How do I prove that then $f(x) = 1$ for some $x ∈ [0, 1]$?
74100
How do you solve $f'(x) = f(f(x))$?
19474
Find all solutions to the functional equation $f(x) +f(x+y)=y+2 $
103251
Solution(s) to $f(x + y) = f(x) + f(y)$ (and miscellaneous questions...)
153510
Questions about the existence of a function
72769
How find this function $xf(x^2)=f(x),x>0$
133646
real analysis -functional equation
124808
How to find inverse of function?
99917
What function satisfies $F'(x) = F(2x)$?
120170
A late-diverging "approximating solution" for a system of functional equations
144090
How to solve the functional equation $f\left(x^2+f(y)\right)=y+f(x)^2$