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.

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Found problems: 787

1999 Greece National Olympiad, 1
Tags: quadratics , inequalities proposed , inequalities
Let $f(x)=ax^2+bx+c$, where $a,b,c$ are nonnegative real numbers, not all equal to zero. Prove that $f(xy)^2\le f(x^2)f(y^2)$ for all real numbers $x,y$.

2014 Moldova Team Selection Test, 2
Tags: inequalities , inequalities proposed
Let $a,b,c$ be positive real numbers such that $abc=1$. Determine the minimum value of $E(a,b,c) = \sum \dfrac{a^3+5}{a^3(b+c)}$ .

2013 Turkey Team Selection Test, 3
Tags: inequalities , trigonometry , inequalities proposed
For all real numbers $x,y,z$ such that $-2\leq x,y,z \leq 2$ and $x^2+y^2+z^2+xyz = 4$, determine the least real number $K$ satisfying \[\dfrac{z(xz+yz+y)}{xy+y^2+z^2+1} \leq K.\]

2008 Romania National Olympiad, 2
Tags: inequalities , inequalities proposed
a) Prove that \[ \dfrac{1}{2} \plus{} \dfrac{1}{3} \plus{} ... \plus{} \dfrac{1}{2^{2n}} > n, \] for all positive integers $ n$. b) Prove that for every positive integer $ n$ we have $ \min\left\{ k \in \mathbb{Z}, k\geq 2 \mid \dfrac{1}{2} \plus{} \dfrac{1}{3} \plus{} \cdots \plus{} \dfrac{1}{k}>n \right\} > 2^n$.

2012 ELMO Shortlist, 2
Tags: inequalities , inequalities proposed
Let $a,b,c$ be three positive real numbers such that $ a \le b \le c$ and $a+b+c=1$. Prove that \[\frac{a+c}{\sqrt{a^2+c^2}}+\frac{b+c}{\sqrt{b^2+c^2}}+\frac{a+b}{\sqrt{a^2+b^2}} \le \frac{3\sqrt{6}(b+c)^2}{\sqrt{(a^2+b^2)(b^2+c^2)(c^2+a^2)}}.\] [i]Owen Goff.[/i]

1995 Hungary-Israel Binational, 3
Tags: algebra , polynomial , inequalities proposed , inequalities
The polynomial $ f(x)\equal{}ax^2\plus{}bx\plus{}c$ has real coefficients and satisfies $ \left|f(x)\right|\le 1$ for all $ x\in [0, 1]$. Find the maximal value of $ |a|\plus{}|b|\plus{}|c|$.

2013 Bosnia Herzegovina Team Selection Test, 5
Tags: inequalities proposed , inequalities
Let $x_1,x_2,\ldots,x_n$ be nonnegative real numbers of sum equal to $1$. Let $F_n=x_1^{2}+x_2^{2}+\cdots +x_n^{2}-2(x_1x_2+x_2x_3+\cdots +x_nx_1)$. Find: a) $\min F_3$; b) $\min F_4$; c) $\min F_5$.

2005 Balkan MO, 3
Tags: inequalities , LaTeX , inequalities proposed
Let $a,b,c$ be positive real numbers. Prove the inequality \[\frac{a^2}{b}+\frac{b^2}{c}+\frac{c^2}{a}\geq a+b+c+\frac{4(a-b)^2}{a+b+c}.\] When does equality occur?

1999 Polish MO Finals, 2
Tags: inequalities , integration , function , triangle inequality , inequalities proposed
Prove that for any $ 2n$ real numbers $ a_{1}$, $ a_{2}$, ..., $ a_{n}$, $ b_{1}$, $ b_{2}$, ..., $ b_{n}$, we have $ \sum_{i < j}{\left|a_{i}\minus{}a_{j}\right|}\plus{}\sum_{i < j}{\left|b_{i}\minus{}b_{j}\right|}\leq\sum_{i,j\in\left[1,n\right]}{\left|a_{i}\minus{}b_{j}\right|}$.

1989 Federal Competition For Advanced Students, 3
Tags: inequalities proposed , inequalities
Let $ a$ be a real number. Prove that if the equation $ x^2\minus{}ax\plus{}a\equal{}0$ has two real roots $ x_1$ and $ x_2$, then: $ x_1^2\plus{}x_2^2 \ge 2(x_1\plus{}x_2).$

2013 Federal Competition For Advanced Students, Part 2, 4
Tags: inequalities , function , induction , inequalities proposed
For a positive integer $n$, let $a_1, a_2, \ldots a_n$ be nonnegative real numbers such that for all real numbers $x_1>x_2>\ldots>x_n>0$ with $x_1+x_2+\ldots+x_n<1$, the inequality $\sum_{k=1}^na_kx_k^3<1$ holds. Show that \[na_1+(n-1)a_2+\ldots+(n-j+1)a_j+\ldots+a_n\leqslant\frac{n^2(n+1)^2}{4}.\]

1970 IMO Longlists, 24
Tags: factorial , inequalities , inequalities proposed
Let $\{n,p\}\in\mathbb{N}\cup \{0\}$ such that $2p\le n$. Prove that $\frac{(n-p)!}{p!}\le \left(\frac{n+1}{2}\right)^{n-2p}$. Determine all conditions under which equality holds.

2009 Greece National Olympiad, 3
Tags: calculus , inequalities , inequalities proposed
Let $ x,y,z$ be nonnegative real numbers such that $ x \plus{} y \plus{} z \equal{} 2$. Prove that $ x^{2}y^{2} \plus{} y^{2}z^{2} \plus{} z^{2}x^{2} \plus{} xyz\leq 1$. When does the equality occur?

2000 Korea - Final Round, 3
Tags: inequalities , search , inequalities proposed
The real numbers $a,b,c,x,y,$ and $z$ are such that $a>b>c>0$ and $x>y>z>0$. Prove that \[\frac {a^2x^2}{(by+cz)(bz+cy)}+\frac{b^2y^2}{(cz+ax)(cx+az)}+\frac{c^2z^2}{(ax+by)(ay+bx)}\ge \frac{3}{4}\]

2011 Iran Team Selection Test, 10
Tags: inequalities , calculus , inequalities proposed
Find the least value of $k$ such that for all $a,b,c,d \in \mathbb{R}$ the inequality \[ \begin{array} c \sqrt{(a^2+1)(b^2+1)(c^2+1)} +\sqrt{(b^2+1)(c^2+1)(d^2+1)} +\sqrt{(c^2+1)(d^2+1)(a^2+1)} +\sqrt{(d^2+1)(a^2+1)(b^2+1)} \\ \ \\ \ge 2( ab+bc+cd+da+ac+bd)-k \end{array}\] holds.

2004 Junior Balkan MO, 1
Tags: inequalities , analytic geometry , calculus , inequalities proposed , algebra
Prove that the inequality \[ \frac{ x+y}{x^2-xy+y^2 } \leq \frac{ 2\sqrt 2 }{\sqrt{ x^2 +y^2 } } \] holds for all real numbers $x$ and $y$, not both equal to 0.

2011 Kosovo National Mathematical Olympiad, 3
Tags: function , trigonometry , inequalities , calculus , algebra , system of equations , inequalities proposed
Find maximal value of the function $f(x)=8-3\sin^2 (3x)+6 \sin (6x)$

1979 IMO Longlists, 61
Tags: function , inequalities proposed , inequalities
There are two non-decreasing sequences $\{a_i\}$ and $\{b_i\}$ of $n$ real numbers each, such that $a_i\le a_{i+1}$ for each $1\le i\le n-1$, and $b_i\le b_{i+1}$ for each $1\le i\le n-1$, and $\sum_{k=1}^{m}{a_k}\ge \sum_{k=1}^{m}{b_k}$ where $m\le n$ with equality for $m=n$. For a convex function $f$ defined on the real numbers, prove that $\sum_{k=1}^{n}{f(a_k)}\le \sum_{k=1}^{n}{f(b_k)}$.

2004 India IMO Training Camp, 3
Tags: inequalities , inequalities proposed
For $a,b,c$ positive reals find the minimum value of \[ \frac{a^2+b^2}{c^2+ab}+\frac{b^2+c^2}{a^2+bc}+\frac{c^2+a^2}{b^2+ca}. \]

2009 Turkey MO (2nd round), 2
Tags: inequalities , calculus , derivative , function , inequalities proposed
Show that \[ \frac{(b+c)(a^4-b^2c^2)}{ab+2bc+ca}+\frac{(c+a)(b^4-c^2a^2)}{bc+2ca+ab}+\frac{(a+b)(c^4-a^2b^2)}{ca+2ab+bc} \geq 0 \] for all positive real numbers $a, \: b , \: c.$

1997 Federal Competition For Advanced Students, Part 2, 1
Tags: inequalities , inequalities proposed
Determine all quadruples $(a, b, c, d)$ of real numbers satisfying the equation \[256a^3b^3c^3d^3 = (a^6+b^2+c^2+d^2)(a^2+b^6+c^2+d^2)(a^2+b^2+c^6+d^2)(a^2+b^2+c^2+d^6).\]

1983 IMO Longlists, 48
Tags: inequalities , geometry , parallelogram , inequalities proposed
Prove that in any parallelepiped the sum of the lengths of the edges is less than or equal to twice the sum of the lengths of the four diagonals.

2010 Contests, 1
Tags: inequalities , inequalities proposed
Let $a,b$ be real numbers. Prove the inequality \[ 2(a^4+a^2b^2+b^4)\ge 3(a^3b+ab^3).\]

2007 Nicolae Coculescu, 2
Tags: inequalities , inequalities proposed
Let be $ a,b,c\in (0,\infty)$ such that $ 3abc\equal{}1$ . Show that : $ \frac{3a^5}{3a^5\plus{}2bc}\plus{}\frac{3b^5}{3b^5\plus{}2ca}\plus{}\frac{3c^5}{3c^5\plus{}2ab}\ge 1$

2010 Iran MO (3rd Round), 2
Tags: inequalities , search , inequalities proposed
$a,b,c$ are positive real numbers. prove the following inequality: $\frac{1}{a^2}+\frac{1}{b^2}+\frac{1}{c^2}+\frac{1}{(a+b+c)^2}\ge \frac{7}{25}(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}+\frac{1}{a+b+c})^2$ (20 points)