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Newton Sums (Sym Poly Part 2) Week#7

Well..  I was asked to prove Newton Sums, so since I latexed the proof, why not post it :P. Newton Sums: Consider a polynomial $P(x)$ of degree $n$, with roots $x_1,x_2,\dots,x_n$ $$P(x) = a_nx^n + a_{n-1}x^{n-1} + \cdots + a_1x + a_0.$$  Define $p_d=x_1^d+\dots+x_n^d.$ Then we have,   $$a_np_1 + a_{n-1} = 0$$  $$a_np_2 + a_{n-1}p_1 + 2a_{n-2}=0$$ $$a_np_3 + a_{n-1}p_2 + a_{n-2}p_1 + 3a_{n-3}=0$$ $$\vdots$$ (Define $a_j = 0$ for $j<0$.) Proof : Note that $$p_1=x_1+x_2+\dots+x_n=\frac{-a_{n-1}}{a_n}\implies \boxed{a_n\cdot p_1+a_{n-1}=0}$$ Note that $$p_2=x_1^2+\dots+x_n^2=(x_1+\dots+x_n)^2-2(x_1\cdot x_2+x_1\cdot x_3+\dots+x_{n-1}\cdot x_{n})=$$ $$p_1 \cdot \frac{-a_{n-1}}{a_n}-2\cdot \frac{a_{n-2}}{a_n}\implies \boxed{p_2\cdot a_n+p_1\cdot a_{n-1}+2\cdot a_{n-2}=0}$$ Note that $$p_3=x_1^3+\dots+x_n^3=(x_1^2+\dots+x_n^2)(x_1+\dots+x_n)-(x_1\cdot x_2+x_1\cdot x_3+\dots+$$ $$ x_{n-1}\cdot x_{n})(x_1+x_2+\dots+x_n)+3(x_1\cdot x_2\cdot x_3+\dots+x_{n-2}\cdot x_...

TOP 10 problems of Week#2

This week was full Number Theory and algebra biased!! 😄 Do try all the problems first!! And if you guys get any nice solutions , do post in the comments section! Here are the walkthroughs of this week's top 5 Number Theory problems! 5th position (1999 JBMO P2):  For each nonnegative integer $n$ we define $A_n = 2^{3n}+3^{6n+2}+5^{6n+2}$. Find the greatest common divisor of the numbers $A_0,A_1,\ldots, A_{1999}$. Walkthrough: It doesn't require a walkthrough, I wrote this here, cause it's a cute problem for the person who has just started Contest math :P a. What is $A_0$? b. Find out $A_1$. c. Show that $\boxed{7}$ is the required answer! 4th position (APMO, Evan Chen's orders modulo a prime handout):   Let $a,b,c$ be distinct integers. Given that $a | bc + b + c, b | ca + c + a$ and $c | ab + a + b$, prove that at least one of $a, b, c$ is not prime. Walkthrough: Fully thanks to  MSE  ! (Also one should try MSE, it has helped me a lot, ofc it's more tilted to Colle...