This website contains problems from math contests. Problems and corresponding tags were obtained from the Art of Problem Solving website.

Tags were heavily modified to better represent problems.

AND:
OR:
NO:

Found problems: 1269

1990 China Team Selection Test, 4
Tags: function , algebra unsolved , algebra
Number $a$ is such that $\forall a_1, a_2, a_3, a_4 \in \mathbb{R}$, there are integers $k_1, k_2, k_3, k_4$ such that $\sum_{1 \leq i < j \leq 4} ((a_i - k_i) - (a_j - k_j))^2 \leq a$. Find the minimum of $a$.

1997 Vietnam Team Selection Test, 2
Tags: logarithms , algebra unsolved , algebra
Find all pairs of positive real numbers $ (a, b)$ such that for every $ n \in\mathbb{N}^*$ and every real root $ x_n$ of the equation $ 4n^2x \equal{} \log_2(2n^2x \plus{} 1)$ we always have $ a^{x_n} \plus{} b^{x_n} \ge 2 \plus{} 3x_n$.

2005 MOP Homework, 2
Tags: algebra , polynomial , algebra unsolved
Determine if there exist four polynomials such that the sum of any three of them has a real root while the sum of any two of them does not.

1987 China Team Selection Test, 3
Tags: induction , algebra unsolved , algebra
Let $r_1=2$ and $r_n = \prod^{n-1}_{k=1} r_i + 1$, $n \geq 2.$ Prove that among all sets of positive integers such that $\sum^{n}_{k=1} \frac{1}{a_i} < 1,$ the partial sequences $r_1,r_2, ... , r_n$ are the one that gets nearer to 1.

2000 Taiwan National Olympiad, 3
Tags: function , induction , algebra unsolved , algebra
Define a function $f:\mathbb{N}\rightarrow\mathbb{N}_0$ by $f(1)=0$ and \[f(n)=\max_j\{ f(j)+f(n-j)+j\}\quad\forall\, n\ge 2 \] Determine $f(2000)$.

1983 Federal Competition For Advanced Students, P2, 1
Tags: algebra unsolved , algebra
For every natural number $ x$, let $ Q(x)$ be the sum and $ P(x)$ the product of the (decimal) digits of $ x$. Show that for each $ n \in \mathbb{N}$ there exist infinitely many values of $ x$ such that: $ Q(Q(x))\plus{}P(Q(x))\plus{}Q(P(x))\plus{}P(P(x))\equal{}n$.

1996 China Team Selection Test, 2
Tags: function , limit , induction , strong induction , algebra unsolved , algebra
$S$ is the set of functions $f:\mathbb{N} \to \mathbb{R}$ that satisfy the following conditions: [b]I.[/b] $f(1) = 2$ [b]II.[/b] $f(n+1) \geq f(n) \geq \frac{n}{n + 1} f(2n)$ for $n = 1, 2, \ldots$ Find the smallest $M \in \mathbb{N}$ such that for any $f \in S$ and any $n \in \mathbb{N}, f(n) < M$.

2013 Iran MO (3rd Round), 7
Tags: algebra , polynomial , algebra unsolved
An equation $P(x)=Q(y)$ is called [b]Interesting[/b] if $P$ and $Q$ are polynomials with degree at least one and integer coefficients and the equations has an infinite number of answers in $\mathbb{N}$. An interesting equation $P(x)=Q(y)$ [b]yields in[/b] interesting equation $F(x)=G(y)$ if there exists polynomial $R(x) \in \mathbb{Q} [x]$ such that $F(x) \equiv R(P(x))$ and $G(x) \equiv R(Q(x))$. (a) Suppose that $S$ is an infinite subset of $\mathbb{N} \times \mathbb{N}$.$S$ [i]is an answer[/i] of interesting equation $P(x)=Q(y)$ if each element of $S$ is an answer of this equation. Prove that for each $S$ there's an interesting equation $P_0(x)=Q_0(y)$ such that if there exists any interesting equation that $S$ is an answer of it, $P_0(x)=Q_0(y)$ yields in that equation. (b) Define the degree of an interesting equation $P(x)=Q(y)$ by $max\{deg(P),deg(Q)\}$. An interesting equation is called [b]primary[/b] if there's no other interesting equation with lower degree that yields in it. Prove that if $P(x)=Q(y)$ is a primary interesting equation and $P$ and $Q$ are monic then $(deg(P),deg(Q))=1$. Time allowed for this question was 2 hours.

2010 Romania National Olympiad, 3
Tags: floor function , algebra unsolved , algebra
For any integer $n\ge 2$ denote by $A_n$ the set of solutions of the equation \[x=\left\lfloor\frac{x}{2}\right\rfloor+\left\lfloor\frac{x}{3}\right\rfloor+\cdots+\left\lfloor\frac{x}{n}\right\rfloor .\] a) Determine the set $A_2\cup A_3$. b) Prove that the set $A=\bigcup_{n\ge 2}A_n$ is finite and find $\max A$. [i]Dan Nedeianu & Mihai Baluna[/i]

1989 India National Olympiad, 1
Tags: algebra , polynomial , calculus , integration , quadratics , modular arithmetic , algebra unsolved
Prove that the Polynomial $ f(x) \equal{} x^{4} \plus{} 26x^{3} \plus{} 56x^{2} \plus{} 78x \plus{} 1989$ can't be expressed as a product $ f(x) \equal{} p(x)q(x)$ , where $ p(x)$ and $ q(x)$ are both polynomial with integral coefficients and with degree at least $ 1$.

2013 Moldova Team Selection Test, 2
Tags: algebra unsolved , algebra
Find all pairs of real numbers $(x,y)$ satisfying $\left\{\begin{array}{rl} 2x^2+xy &=1 \\ \frac{9x^2}{2(1-x)^4}&=1+\frac{3xy}{2(1-x)^2} \end{array}\right.$

2010 Romania National Olympiad, 1
Tags: quadratics , Vieta , function , algebra , algebra unsolved
Let $(a_n)_{n\ge0}$ be a sequence of positive real numbers such that \[\sum_{k=0}^nC_n^ka_ka_{n-k}=a_n^2,\ \text{for any }n\ge 0.\] Prove that $(a_n)_{n\ge0}$ is a geometric sequence. [i]Lucian Dragomir[/i]

2015 IFYM, Sozopol, 3
Tags: function , algebra unsolved , algebra
Find all functions $f:\mathbb R^{+} \longrightarrow \mathbb R^{+}$ so that $f(xy + f(x^y)) = x^y + xf(y)$ for all positive reals $x,y$.

2012 IFYM, Sozopol, 3
Tags: algebra , polynomial , algebra unsolved
The polynomial $p(x)$ is of degree $9$ and $p(x)-1$ is exactly divisible by $(x-1)^{5}$. Given that $p(x) + 1$ is exactly divisible by $(x+1)^{5}$, find $p(x)$.

2014 Iran Team Selection Test, 2
Tags: algebra , polynomial , number theory , algebra unsolved
find all polynomials with integer coefficients that $P(\mathbb{Z})= ${$p(a):a\in \mathbb{Z}$} has a Geometric progression.

2009 Romanian Masters In Mathematics, 1
Tags: floor function , inequalities , number theory , greatest common divisor , least common multiple , triangle inequality , algebra unsolved
For $ a_i \in \mathbb{Z}^ \plus{}$, $ i \equal{} 1, \ldots, k$, and $ n \equal{} \sum^k_{i \equal{} 1} a_i$, let $ d \equal{} \gcd(a_1, \ldots, a_k)$ denote the greatest common divisor of $ a_1, \ldots, a_k$. Prove that $ \frac {d} {n} \cdot \frac {n!}{\prod\limits^k_{i \equal{} 1} (a_i!)}$ is an integer. [i]Dan Schwarz, Romania[/i]

2011 Kazakhstan National Olympiad, 1
Tags: logarithms , algebra unsolved , algebra
Given a real number $a> 0$. How many positive real solutions of the equation is $ a^{x}=x^{a} $

2002 Austrian-Polish Competition, 8
Tags: trigonometry , limit , inequalities , algebra unsolved , algebra
Determine the number of real solutions of the system \[\left\{ \begin{aligned}\cos x_{1}&= x_{2}\\ &\cdots \\ \cos x_{n-1}&= x_{n}\\ \cos x_{n}&= x_{1}\\ \end{aligned}\right.\]

2007 Hong Kong TST, 2
Tags: trigonometry , algebra unsolved , algebra
[url=http://www.mathlinks.ro/Forum/viewtopic.php?t=107262]IMO 2007 HKTST 1[/url] Problem 2 Let $A$, $B$ and $C$ be real numbers such that (i) $\sin A \cos B+|\cos A \sin B|=\sin A |\cos A|+|\sin B|\cos B$, (ii) $\tan C$ and $\cot C$ are defined. Find the minimum value of $(\tan C-\sin A)^{2}+(\cot C-\cos B)^{2}$.

1986 Bundeswettbewerb Mathematik, 3
Tags: algebra unsolved , algebra
Let $d_n$ be the last digit, distinct from 0, in the decimal expansion of $n!$. Prove that the sequence $d_1,d_2,d_3, \ldots$ is not periodic.

2010 China Team Selection Test, 2
Tags: algebra , polynomial , function , complex numbers , algebra unsolved
Let $A=\{a_1,a_2,\cdots,a_{2010}\}$ and $B=\{b_1,b_2,\cdots,b_{2010}\}$ be two sets of complex numbers. Suppose \[\sum_{1\leq i<j\leq 2010} (a_i+a_j)^k=\sum_{1\leq i<j\leq 2010}(b_i+b_j)^k\] holds for every $k=1,2,\cdots, 2010$. Prove that $A=B$.

2005 MOP Homework, 5
Tags: function , integration , calculus , algebra , binomial theorem , algebra unsolved
Show that for nonnegative integers $m$ and $n$, $\frac{\dbinom{m}{0}}{n+1}-\frac{\dbinom{m}{1}}{n+2}+...+(-1)^m\frac{\dbinom{m}{m}}{n+m+1}$ $=\frac{\dbinom{n}{0}}{m+1}-\frac{\dbinom{n}{1}}{m+2}+...+(-1)^n\frac{\dbinom{n}{n}}{m+n+1}$.

2013 South africa National Olympiad, 4
Tags: algebra , polynomial , algebra unsolved
Determine all pairs of polynomials $f$ and $g$ with real coefficients such that \[ x^2 \cdot g(x) = f(g(x)). \]

2014 Contests, 2
Tags: algebra , polynomial , number theory , algebra unsolved
find all polynomials with integer coefficients that $P(\mathbb{Z})= ${$p(a):a\in \mathbb{Z}$} has a Geometric progression.

2005 All-Russian Olympiad, 2
Tags: calculus , integration , quadratics , algebra unsolved , algebra
Find the number of subsets $A\subset M=\{2^0,\,2^1,\,2^2,\dots,2^{2005}\}$ such that equation $x^2-S(A)x+S(B)=0$ has integral roots, where $S(M)$ is the sum of all elements of $M$, and $B=M\setminus A$ ($A$ and $B$ are not empty).