Differentiability of $f(x+y) = \frac{f(x)+f(y)}{1-f(x)f(y)}$
111470
Proof of differentiability of $f(x)$
112859
$f(x,y) = \frac{x^3y}{x^4 + y^2}$ is not differentiable at $(0,0)$.
154881
Question on differentiability of a continuous function
28286
About finding the function such that $f(xy)=f(x)f(y)-f(x+y)+1$
61782
How to prove that $f(x) = \frac{-2x+1}{(2x-1)^2-1}$ is one-to-one on $(0,1)$?
125788
A function with a property $f(x+y)=f(x)f(y)$
124346
Where is $f(z)=\Re (z)$ differentiable?
142682
Find $f(x)$ where $ f(x)+f\left(\frac{1-x}x\right)=x$
71738
Continuously differentiable function iff $|f(x + h) - f(x + t) - l(h - t)| \leq \epsilon |h-t|$
129856
Show that $f(x)=\frac{x}{1+|x|}$ is uniformly continuous.
53024
$f(x)f(1/x)=f(x)+f(1/x)$
33130
$f$ differentiable except in $1$ point
122003
From the limit definition of differentiability, determine where the function $f(x) = \sqrt{x}$ is differentiable?
14952
Prove: $\frac{x}{\sqrt{y}}+\frac{y}{\sqrt{x}}\geq \sqrt{x}+\sqrt{y}$
85623
Proof of continuity implied by differentiability
73073
Differentiating $y=x^{2}$
4636
How to show that $f$ is differentiable at $x=0.$