Show that $(x^2 + y^2) \sin\left(\frac{1}{x^2 + y^2}\right)$ is differentiable.
46398
Is $(x^2+y^2+z^2) \ \sin \frac{1}{\sqrt{x^2+y^2+z^2}}$ Differentiable in $(0,0,0)$?
80553
Show that,$\int_0^\pi \left|\frac{\sin nx}{x}\right|\mathrm{d}x \ge \frac{2}{\pi}\left(1+\frac12+\cdots+\frac{1}{n}\right)$
39057
Check the differentiablity of $\theta :\mathbb R^2 \setminus\{(0,0)\}\to \mathbb R$
96973
If $F(0,0)=0$ and $F(x,y)= \frac{xy}{x^2+y^2}$ for $(x,y)\neq (0,0)$ then $F$ is differentiable at $(0,0)$?
127449
Uniform continuous of $f(x,y) = \sin(x^2+y)$
82961
Show that $\left| \frac{1}{x}-\frac{1}{z} \right| \le \left|\frac{1}{x} - \frac{1}{y} \right| + \left|\frac{1}{y} - \frac{1}{z} \right|$.
105047
Prove the inequality $|xy|\leq\frac{1}{2}(x^2+y^2)$
143491
Show that $f$ is differentiable on $(−1, 1)$.
85480
Let $f(x,y)=\frac{x^3-y^3}{x^2+y^2}$. Is f differentiable in $(0,0)$?
14548
Multivariable limit $\frac{(2x^2)y}{x^4+y^2}$
143375
Showing that $\lim_{(x,y) \to (0, 0)}\frac{xy^2}{x^2+y^2} = 0$
98462
Prove the inverse of a strictly increasing function is differentiable.
121548
proof of an inequality $ \left( 1+ \frac{x}{p} \right) ^{p}$
106742
Evaluating $ \lim_{x \rightarrow 0}\left (\frac{\sin(x)}{x}\right)^\frac{1}{x^2}$
85623
Proof of continuity implied by differentiability
94869
Show that $ \int_{k}^{2} \frac{1}{f(y)} =1$
109994
Show discontinuity of $\frac{xy}{x^2+y^2}$