Find all "tame" solutions of $f(x+y)+f(x-y)=2(f(x)+f(y))$
109942
Find continuous functions such that $f(x+y)+f(x-y)=2[f(x)+f(y)]$
86128
Find all functions $ f : \Bbb R \to \Bbb R$ which satisfy $f(x)f(y) = f(x + y) + xy$ for all $x, y ∈ \Bbb R$.
45616
Find all solutions of ${\frac {1} {x} } + {\frac {1} {y} } +{\frac {1} {z}}=1$, where $x$, $y$ and $z$ are positive integers
49794
Solve $f(x^2+y+f(y))=2y+f(x)^2$ over $\mathbb{R}$
98255
Find $f(x)$ such that $f(f(x)) = x^2 - 2$
64339
Find $f$ where $f'(x) = f(1+x)$
10753
Natural number solutions to $\frac{xy}{x+y}=n$ (equivalent to $\frac 1x+\frac 1y=\frac 1n$)
14773
Finding distinct solutions for the equation
409
functions satisfying $f(x - y) = f(x) f(y) - f(a - x) f(a + y)$ and $f(0)=1$
62966
Find all functions $f(x)$ such that $f\left(x^2+f(y)\right)$=$y+(f(x))^2$
73519
Determine all functions satisfying $f(x + f(x + y)) + f(xy) = x + f(x + y) +yf(x)$
157744
Cauchy's functional equation with composite function: $gf(x+y)=gf(x)+gf(y)$
48652
Solve the functional equation $2f(x)=f(ax)$ for some $a$.
136475
d'Alembert-like functional equation: $f(x+y)+g(x-y)=\lambda f(x)g(y)$
42699
Solve for $f(x)$ if $f(f(x))=6x-f(x)$
76679
Prove there are no other solutions of functional equation $f(x+y) = \frac{f(x)+f(y)}{1-f(x)f(y)}$
19019
Find all functions $f:\Bbb{Q}\rightarrow \Bbb{Q}$ such that $f(x)+f(t)=f(y)+f(z)$ for all rational numbers $x<y<z<t$ that form an AP