Functional Equations Problem
66772
$f(f(x)f(y))+f(x+y)=f(xy)$
103251
Solution(s) to $f(x + y) = f(x) + f(y)$ (and miscellaneous questions...)
114270
How do I solve this equation?
97994
Orthogonality Relations Exercise, Brezis' Book Functional Analysis
142232
Functional Analysis. Continuous extensions of linear functionals.
12240
Problem with a continuous function
76679
Prove there are no other solutions of functional equation $f(x+y) = \frac{f(x)+f(y)}{1-f(x)f(y)}$
34888
An MCQ for finding the extremal of the functional $J = \int_{a}^{b} F(x, y, y^{'})$
157744
Cauchy's functional equation with composite function: $gf(x+y)=gf(x)+gf(y)$
14773
Finding distinct solutions for the equation
133646
real analysis -functional equation
47212
Solving functional equation
131586
Hard functional equation: $ f \big ( x y + f ( x ) \big) = f \big( f ( x ) f ( y ) \big) + x $
144090
How to solve the functional equation $f\left(x^2+f(y)\right)=y+f(x)^2$
32432
Strategies to find the set of functions $f:\mathbb R\to\mathbb R$ satisfing the functional equation: $f(x^3)+f(y^3)=(x+y)(f(x^2)+f(y^2)-f(xy))$
111789
Solving functional differential equation $f'(x)=2f(2x)-f(x)$
156778
Finding functions satisfying $f(f(x))+f(x)+x=0$