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 7 Is there limit $\lim_{(x,y) \to (0,0)} \frac{x^3}{x^2 + y^2}$? 6 If $(\nabla f(x)-\nabla f(y))\cdot(x-y)\geq m(x-y)\cdot(x-y)$, why is $f$ convex? 5 $(0 \leq f' \leq f$ on $\mathbb R$ and $f(a)=0)$ $\implies f=0$? 5 A difficulty solving a limit 5 Prove $\frac {1}{\cos 0^\circ \cdot \cos 1^\circ} + \ldots +\frac {1}{\cos 88^\circ \cdot \cos 89^\circ}= \frac{\cos 1^\circ}{\sin 1^\circ}$

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 9 supremum of $\int |\int f(x)-f(y)\,dy| \,dx$. 1 Convergence of sequence of probabilities (competition problem) 0 behavior of function at infinite

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