Olympiad problems

2010 Bosnia and Herzegovina Junior BMO TST, 2

Let us consider every third degree polynomial $P(x)$ with coefficients as nonnegative positive integers such that $P(1)=20$. Among them determine polynomial for which is: $a)$ Minimal value of $P(4)$ $b)$ Maximal value of $P(3)/P(2)$

1990 IMO Longlists, 5

Tags: triangle , geometry , minimization , angle

Given the condition that there exist exactly $1990$ triangles $ABC$ with integral side-lengths satisfying the following conditions: (i) $\angle ABC =\frac 12 \angle BAC;$ (ii) $AC = b.$ Find the minimal value of $b.$

2001 IMO Shortlist, 3

Tags: geometry , parallelogram , minimization , triangle

Let $ABC$ be a triangle with centroid $G$. Determine, with proof, the position of the point $P$ in the plane of $ABC$ such that $AP{\cdot}AG + BP{\cdot}BG + CP{\cdot}CG$ is a minimum, and express this minimum value in terms of the side lengths of $ABC$.

1987 IMO Shortlist, 5

Tags: geometry , circumcircle , triangle , minimization , circumcenter

Find, with proof, the point $P$ in the interior of an acute-angled triangle $ABC$ for which $BL^2+CM^2+AN^2$ is a minimum, where $L,M,N$ are the feet of the perpendiculars from $P$ to $BC,CA,AB$ respectively. [i]Proposed by United Kingdom.[/i]

1981 IMO, 1

Tags: trigonometry , incenter , geometric inequality , minimization , geometry

Consider a variable point $P$ inside a given triangle $ABC$. Let $D$, $E$, $F$ be the feet of the perpendiculars from the point $P$ to the lines $BC$, $CA$, $AB$, respectively. Find all points $P$ which minimize the sum \[ {BC\over PD}+{CA\over PE}+{AB\over PF}. \]

1982 IMO Longlists, 17

Tags: sequence , maximization , minimization , rearrangement , algebra

[b](a)[/b] Find the rearrangement $\{a_1, \dots , a_n\}$ of $\{1, 2, \dots, n\}$ that maximizes \[a_1a_2 + a_2a_3 + \cdots + a_na_1 = Q.\] [b](b)[/b] Find the rearrangement that minimizes $Q.$

1983 IMO Shortlist, 17

Tags: geometry , geometric inequality , optimization , minimization , maximization , point set

Let $P_1, P_2, \dots , P_n$ be distinct points of the plane, $n \geq 2$. Prove that \[ \max_{1\leq i<j\leq n} P_iP_j > \frac{\sqrt 3}{2}(\sqrt n -1) \min_{1\leq i<j\leq n} P_iP_j \]

1989 IMO Longlists, 84

Tags: maximization , minimization , optimization , algebra , calculus

Let $ n \in \mathbb{Z}^\plus{}$ and let $ a, b \in \mathbb{R}.$ Determine the range of $ x_0$ for which \[ \sum^n_{i\equal{}0} x_i \equal{} a \text{ and } \sum^n_{i\equal{}0} x^2_i \equal{} b,\] where $ x_0, x_1, \ldots , x_n$ are real variables.

2001 China Team Selection Test, 3

Tags: algebra , function , calculus , polynomial , minimization

Let $F = \max_{1 \leq x \leq 3} |x^3 - ax^2 - bx - c|$. When $a$, $b$, $c$ run over all the real numbers, find the smallest possible value of $F$.

1981 IMO Shortlist, 15

Tags: trigonometry , geometry , incenter , geometric inequality , minimization

Consider a variable point $P$ inside a given triangle $ABC$. Let $D$, $E$, $F$ be the feet of the perpendiculars from the point $P$ to the lines $BC$, $CA$, $AB$, respectively. Find all points $P$ which minimize the sum \[ {BC\over PD}+{CA\over PE}+{AB\over PF}. \]