The range of function $f(x,y)=\frac{x+y}{1+x^2+y^2}$
99024
Let $\,E=\{(x,y) \in \Bbb R^2: |x| \le 1,|y|\le 1\}.$
73786
Limit of $\frac{\sin(x+y)}{x+y}$ as $(x,y) \to (0,0)$
23294
Show that the function $f = \frac{xy}{x^2 + y^2}$ is continuous along every horizontal and every vertical line
151297
Second order partial of $f(x,y)=\frac{xy(x^2-y^2)}{x^2+y^2}$
105062
Prove that the range of the entire function $z^2+\cos(z)$ is all of $\mathbb{C}$.
98255
Find $f(x)$ such that $f(f(x)) = x^2 - 2$
109896
Proving that the function $f(x,y)=\frac{x^2y}{x^2 + y^2}$ with $f(0,0)=0$ is continuous at $(0,0)$.
83557
$\frac{x^2}{y+z}+\frac{y^2}{x+z}+\frac{z^2}{x+y} \ge \frac{1}{2}(x+y+z)$
31146
Does the limit $\lim_{(x,y)\to (0,0)} \frac {x^3y^2}{x^4+y^6}$ exist
43667
Is $f(x,y(x))$ a function of two variables? If so, how is that possible?
87055
How to prove $\frac{x}{1+x^2}0$?
1071
Determine all functions $f:\mathbb{N}\rightarrow\mathbb{N}$ such that $xf(y)+yf(x)=(x+y)f(x^2+y^2)$ for all $x,y\in\mathbb{N}$ (contest question)
55654
Limit of $\frac{x^y-y^x}{x^x-y^y} $ while $x\to y$
409
functions satisfying $f(x - y) = f(x) f(y) - f(a - x) f(a + y)$ and $f(0)=1$
4278
Is $\frac{\vert x+y\vert}{1+\vert x+y\vert}\leq\frac{\vert x\vert}{1+\vert x\vert}+\frac{\vert y\vert}{1+\vert y\vert}$ true?
64339
Find $f$ where $f'(x) = f(1+x)$
94466
evaluating the limit $ \lim_{(x,y) \rightarrow (0,0) } \frac{x^2y^2}{x^2 + y^2} $