# Francesco Sica

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bio website francescosica.org location age member for 1 year, 1 month seen Oct 27 '12 at 16:39 profile views 35

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 Apr23 awarded Yearling Sep6 comment Inequality. $ab^2+bc^2+ca^2 \geq a+b+c.$Iuli's proof is substantially correct and you can prove the second displayed equation using rearrangements. This method doesn't necessarily have to prove symmetric inequalities. You just have to take the correct permutation to get $y^2z+z^2x+x^2y$. For instance, supposing that $y\geq x\geq z$, the same inequality can be proved. Sep5 revised Inequality. $ab^2+bc^2+ca^2 \geq a+b+c.$Typo in the exponent of the first displayed equation. Typo in second equation. Removed the rest, now useless. Sep5 suggested suggested edit on Inequality. $ab^2+bc^2+ca^2 \geq a+b+c.$ Aug28 awarded Good Answer Aug14 comment Primes Not Dividing $\binom{2n}{n}$Any such prime appears exactly twice both in the numerator and the denominator of $\binom{2n}{n}= \frac{(2n)!}{(n!)^2}$. Jun8 awarded Constituent Jun8 awarded Caucus Jun1 comment How to show that if $x_1,\ldots,x_n$ are real numbers, then $|x_1|\ldots|x_n| \le |x_1|^2 + \cdots + |x_n|^2$The right kind of such inequalities should be homogeneous of the same degree on both sides. Here, it is homogeneous of degree $n$ on the left and $2$ on the right. May14 comment Exercise: continuity of a function of two variablesHint: Use uniform continuity of $\phi$ on compact sets. May12 answered UPDATE: How to find the order of elliptic curve over finite field extension May11 awarded Editor May11 revised Cyclic Group Questionsadded 16 characters in body May11 comment Cyclic Group QuestionsYou're right, I forgot when there are no $2$'s at all. I will edit the answer. Thanks! May11 answered Cyclic Group Questions May10 comment calculating the amplitude of a cosine functionWhy the notation $\| A \|$ etc. in the first displayed formula? May10 comment When did Fubini's name get applied to the theorem without measures?Look at the wikipedia entry for Fubini's theorem. I will just add that in Italian universities, the theorem is known as the theorem of Fubini-Tonelli (and pay attention to the spelling, one 'n'). May10 awarded Supporter May5 answered The power series $\sum\limits_{n=1}^{\infty} \frac {z^{n} }{ n^{2}} \$ May2 comment Importance of rigorIt is Littlewood, not Landau, who proved that $\mathrm{li}(x) - \pi(x)$ changes sign infinitely often. The first one to give an upper bound on the range of $x$ when this first happens is Skewes.