Find a function such $f(f(x))=-x$
40070
Is there a real-valued function $f$ such that $f(f(x)) = -x$?
37976
Find all functions $f$ such that $(x+y)f(x)+f(y^2)=(x+y)f(y)+f(x^2)$
28927
IMO 1987 - function such that $f(f(n))=n+1987$
145573
How to show that $f$ is a zero function?
149328
A function such that $f:\mathbb C \to \mathbb C$ such that $f(z)f(iz)=z^2$ satisfies $f(z)+f(-z)=0$.(MADHAVA-2020)
105319
A calculus problem with functions such that $f''(x) = g(x)$ and $g''(x) = f(x)$
77074
If $ f(f(f(x)))=x$, does$ f(x)=x$ necessarily follow?
13042
Finding a function from the given functional equation .
2072
Demonstrate that if $f$ is surjective then $X = f(f^{-1}(X))$
31269
How to visualize $f(x) = (-2)^x$
103568
Possibility of finding a such function?
57938
When do two functions become equal?
82597
How to find $ f(x)$ if $f(1-f(x))=x$ for all $x$ $\in \mathbb{R}$
126931
Find $f(x)$ such that $f(x)+f\left(\frac{1}{x}\right)=f(x)\cdot f\left(\frac{1}{x}\right)$
49211
Solving $f(x+y) = f(x)f(y)f(xy)$
132093
Solve $f(f(x))=f(x)$
124808
How to find inverse of function?