olymmath

ELMO SL 2012 A9

    Let a,b,ca,b,c be distinct positive real numbers, and let kk be a positive integer greater than 33 . Show that ∣ak+1(b−c)+bk+1(c−a)+ck+1(a−b)ak(b−c)+bk(c−a)+ck(a−b)∣≥k+13(k−1)(a+b+c)\left\lvert\frac{a^{k+1}(b-c)+b^{k+1}(c-a)+c^{k+1}(a-b)}{a^k(b-c)+b^k(c-a)+c^k(a-b)}\right\rvert\ge \frac{k+1}{3(k-1)}(a+b+c) and ∣ak+2(b−c)+bk+2(c−a)+ck+2(a−b)ak(b−c)+bk(c−a)+ck(a−b)∣≥(k+1)(k+2)3k(k−1)(a2+b2+c2).\left\lvert\frac{a^{k+2}(b-c)+b^{k+2}(c-a)+c^{k+2}(a-b)}{a^k(b-c)+b^k(c-a)+c^k(a-b)}\right\rvert\ge \frac{(k+1)(k+2)}{3k(k-1)}(a^2+b^2+c^2).

    Calvin Deng.

    Dataset text AI-MO AoPS. Quoted with source.

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