2014 AIME I Problem 6

Attempt Problem 6 of the 2014 AIME I below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2014 AIME I solutions, or check the answer key.

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6.

The graphs y=3(xh)2+jy = 3(x-h)^2 + j and y=2(xh)2+ky = 2(x-h)^2 + k have yy-intercepts of 20132013 and 2014,2014, respectively, and each graph has two positive integer xx-intercepts. Find h.h.

Answer: 36
Concepts:quadraticVieta’s Formulasprime factorization
Difficulty rating: 2450
Solution:

Setting x=0x = 0 gives 3h2+j=20133h^2 + j = 2013 and 2h2+k=2014.2h^2 + k = 2014. Expanding, the first graph is y=3x26hx+2013,y = 3x^2 - 6hx + 2013, whose roots are positive integers with sum 2h2h and product 20133=671=1161.\frac{2013}{3} = 671 = 11 \cdot 61. Similarly the second is y=2x24hx+2014,y = 2x^2 - 4hx + 2014, with integer roots of sum 2h2h and product 20142=1007=1953.\frac{2014}{2} = 1007 = 19 \cdot 53.

The first pair of roots is {11,61}\{11, 61\} or {1,671},\{1, 671\}, so 2h=722h = 72 or 672;672; the second pair is {19,53}\{19, 53\} or {1,1007},\{1, 1007\}, so 2h=722h = 72 or 1008.1008. The only common value is 2h=72,2h = 72, so h=36,h = 36, which indeed gives xx-intercepts 11,6111, 61 and 19,53.19, 53.

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