Olympiad Maths Prep

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Problem 195

AMC 10/12, early questions
Algebra Difficulty 3.7 Find the answer

For some integer mm, the polynomial x32011x+mx^3 - 2011x + m has the three integer roots aa, bb, and cc. Find a+b+c|a| + |b| + |c|.

Official solution

From Vieta's formulas, we know that a+b+c=0a+b+c = 0, and ab+bc+ac=2011ab+bc+ac = -2011. Thus a=(b+c)a = -(b+c). All three of aa, bb, and cc are non-zero: say, if a=0a=0, then b=c=±2011b=-c=\pm\sqrt{2011} (which is not an integer). \textscwlog\textsc{wlog}, let abc|a| \ge |b| \ge |c|. If a>0a > 0, then b,c0b,c 0. We have 2011=ab+bc+ac=a(b+c)+bc=a2+bc-2011=ab+bc+ac = a(b+c)+bc = -a^2+bc
Thus a2=2011+bca^2 = 2011 + bc. We know that bb, cc have the same sign. So a45=2011|a| \ge 45 = \lceil \sqrt{2011} \rceil.
Also, if we fix aa, b+cb+c is fixed, so bcbc is maximized when b=cb = c . Hence, \[2011 = a^2 - bc > \tfrac{3}{4}a^2 \qquad \Longrightarrow \qquad a ^2 4$,
198198 is not divisible by 55, 198/6=33198/6 = 33, which is too small to get 4747.
293/48>6293/48 > 6, 293293 is not divisible by 77 or 88 or 99, we can clearly tell that 1010 is too much.

Hence, a=49|a| = 49, a22011=390a^2 -2011 = 390. b=39b = 39, c=10c = 10.
Answer: 098\boxed{098}

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.