Maths Olympiad Prep

Library / /587 of 860

Algebra Difficulty 5.3 AIME, harder Find the answer

Given that PP is a real polynomial of degree at most 2012 such that P(n)=2nP(n)=2^{n} for n=1,2,,2012n=1,2, \ldots, 2012, what choice(s) of P(0)P(0) produce the minimal possible value of P(0)2+P(2013)2P(0)^{2}+P(2013)^{2} ?

A number or a short expression. Spacing and $ signs are ignored.

Solution

Define \Delta^{1}(n)=P(n+1)-P(n)andΔi(n)=Δi1(n+1)Δi1(n) and \Delta^{i}(n)=\Delta^{i-1}(n+1)-\Delta^{i-1}(n) for i>1i>1. Since P(n)P(n) has degree at most 2012, we know that \Delta^{2012}(n)isconstant.Computing,weobtainΔ1(0)=2P(0) is constant. Computing, we obtain \Delta^{1}(0)=2-P(0) and \Delta^{i}(0)=2^{i-1}for for 1<i \leq 2012.WeseethatcontinuingongivesΔ2012(0)=Δ2012(1)=P(0). We see that continuing on gives \Delta^{2012}(0)=\Delta^{2012}(1)=P(0) and \Delta^{i}(2012-i)=2^{2013-i}for for 1 \leq i \leq 2011.Then,. Then, P(2013)= P(2012)+\Delta^{1}(2012)=\ldots=P(2012)+\Delta^{1}(2011)+\ldots+\Delta^{2012}(0)=P(0)+2^{2013}-2.Now,wewanttominimizethevalueof. Now, we want to minimize the value of P(0)^{2}+P(2013)^{2}=2 P(0)^{2}+2 P(0)\left(2^{2013}-2\right)+\left(2^{2013}-2\right)^{2},butthisoccurssimplywhen, but this occurs simply when P(0)=-\frac{1}{2}\left(2^{2013}-2\right)=1-2^{2012}$.

Want a route through all this instead of an archive? The track puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.

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