Olympiad problems

1989 IMO Longlists, 41

Let $ f(x) \equal{} a \sin^2x \plus{} b \sin x \plus{} c,$ where $ a, b,$ and $ c$ are real numbers. Find all values of $ a, b$ and $ c$ such that the following three conditions are satisfied simultaneously: [b](i)[/b] $ f(x) \equal{} 381$ if $ \sin x \equal{} \frac{1}{2}.$ [b](ii)[/b] The absolute maximum of $ f(x)$ is $ 444.$ [b](iii)[/b] The absolute minimum of $ f(x)$ is $ 364.$

2010 Postal Coaching, 1

Tags: algebra , polynomial , algebra unsolved

A polynomial $P (x)$ with real coeﬃcients and of degree $n \ge 3$ has $n$ real roots $x_1 <x_2 < \cdots < x_n$ such that \[x_2 - x_1 < x_3 - x_2 < \cdots < x_n - x_{n-1} \] Prove that the maximum value of $|P (x)|$ on the interval $[x_1 , x_n ]$ is attained in the interval $[x_{n-1} , x_n ]$.

2015 IFYM, Sozopol, 1

Tags: function , algebra unsolved , algebra

Find all functions $\mathbb R^+\to\mathbb R^+$ such that \[(f(a)+f(b))(f(c)+f(d))=(a+b)(c+d), \quad \forall a,b,c,d\in\mathbb R^+; \quad abcd=1\]

2005 Czech-Polish-Slovak Match, 3

Tags: algebra , polynomial , modular arithmetic , quadratics , algebra unsolved

Find all integers $n \ge 3$ for which the polynomial \[W(x) = x^n - 3x^{n-1} + 2x^{n-2} + 6\] can be written as a product of two non-constant polynomials with integer coefficients.

1982 IMO Longlists, 29

Tags: function , limit , algebra unsolved , algebra

Let $f : \mathbb R \to \mathbb R$ be a continuous function. Suppose that the restriction of $f$ to the set of irrational numbers is injective. What can we say about $f$? Answer the analogous question if $f$ is restricted to rationals.

1995 Vietnam Team Selection Test, 2

Tags: algebra , polynomial , modular arithmetic , search , Rational Root Theorem , algebra unsolved

Find all integers $ k$ such that for infinitely many integers $ n \ge 3$ the polynomial \[ P(x) =x^{n+ 1}+ kx^n - 870x^2 + 1945x + 1995\] can be reduced into two polynomials with integer coefficients.

2006 Estonia Math Open Junior Contests, 6

Tags: geometry , 3D geometry , quadratics , algebra , algebra unsolved

Find all real numbers with the following property: the difference of its cube and its square is equal to the square of the difference of its square and the number itself.

2001 APMO, 4

Tags: analytic geometry , algebra , polynomial , algebra unsolved

A point in the plane with a cartesian coordinate system is called a [i]mixed point[/i] if one of its coordinates is rational and the other one is irrational. Find all polynomials with real coefficients such that their graphs do not contain any mixed point.

1998 Bulgaria National Olympiad, 1

Tags: algebra unsolved , algebra

Let $a_1,a_2,\cdots ,a_n$ be real numbers, not all zero. Prove that the equation: \[\sqrt{1+a_1x}+\sqrt{1+a_2x}+\cdots +\sqrt{1+a_nx}=n\] has at most one real nonzero root.

1988 Polish MO Finals, 1

Tags: function , algebra unsolved , algebra

$d$ is a positive integer and $f : [0,d] \rightarrow \mathbb{R}$ is a continuous function with $f(0) = f(d)$. Show that there exists $x \in [0,d-1]$ such that $f(x) = f(x+1)$.

1998 German National Olympiad, 6a

Tags: algebra , system of equations , powers , symmetry , algebra unsolved , Germany , Real

Find all real pairs $(x,y)$ that solve the system of equations \begin{align} x^5 &= 21x^3+y^3 \\ y^5 &= x^3+21y^3. \end{align}

1998 Bulgaria National Olympiad, 2

Tags: algebra , polynomial , algebra unsolved

The polynomials $P_n(x,y), n=1,2,... $ are defined by \[P_1(x,y)=1, P_{n+1}(x,y)=(x+y-1)(y+1)P_n(x,y+2)+(y-y^2)P_n(x,y)\] Prove that $P_{n}(x,y)=P_{n}(y,x)$ for all $x,y \in \mathbb{R}$ and $n $.

2011 Morocco National Olympiad, 3

Tags: function , algebra unsolved , algebra

Find all functions $f:\mathbb{R}\rightarrow \mathbb{R}$ such that for all $x,y, \in \mathbb{R}$, \[xf(x+xy)=xf(x)+f(x^{2})\cdot f(y).\]

2008 Ukraine Team Selection Test, 12

Tags: algebra , polynomial , induction , algebra unsolved

Prove that for all natural $ m$, $ n$ polynomial $ \sum_{i \equal{} 0}^{m}\binom{n\plus{}i}{n}\cdot x^i$ has at most one real root.

2000 South africa National Olympiad, 3

Tags: induction , algebra unsolved , algebra

Let $c \geq 1$ be an integer, and define the sequence $a_1,\ a_2,\ a_3,\ \dots$ by \[ \begin{aligned} a_1 & = 2, \\ a_{n + 1} & = ca_n + \sqrt{\left(c^2 - 1\right)\left(a_n^2 - 4\right)}\textrm{ for }n = 1,2,3,\dots\ . \end{aligned} \] Prove that $a_n$ is an integer for all $n$.

2002 APMO, 5

Tags: function , induction , algebra unsolved , algebra

Let ${\bf R}$ denote the set of all real numbers. Find all functions $f$ from ${\bf R}$ to ${\bf R}$ satisfying: (i) there are only finitely many $s$ in ${\bf R}$ such that $f(s)=0$, and (ii) $f(x^4+y)=x^3f(x)+f(f(y))$ for all $x,y$ in ${\bf R}$.

1988 USAMO, 2

Tags: AMC , USA(J)MO , USAMO , algebra , polynomial , Vieta , algebra unsolved

The cubic equation $x^3 + ax^2 + bx + c = 0$ has three real roots. Show that $a^2-3b\geq 0$, and that $\sqrt{a^2-3b}$ is less than or equal to the difference between the largest and smallest roots.

2004 India IMO Training Camp, 2

Tags: algebra , polynomial , algebra unsolved

Let $P(x) = x^4 + ax^3 + bx^2 + cx + d$ and $Q(x) = x^2 + px + q$be two real polynomials. Suppose that there exista an interval $(r,s)$ of length greater than $2$ SUCH THAT BOTH $P(x)$ AND $Q(x)$ ARE nEGATIVE FOR $X \in (r,s)$ and both are positive for $x > s$ and $x<r$. Show that there is a real $x_0$ such that $P(x_0) < Q(x_0)$

2011 IFYM, Sozopol, 6

Tags: algebra , polynomial , inequalities , algebra unsolved

Define a sequence {$a_n$}$^{\infty}_{n=1}$ by $a_1 = 4, a_2 = a_3 = (a^2 - 2)^2$ and $a_n = a_{n-1}.a_{n-2} - 2(a_{n-1} + a_{n-2}) - a_{n-3} + 8, n \ge 4$, where $a > 2$ is a natural number. Prove that for all $n$ the number $2 + \sqrt{a_n}$ is a perfect square.

1996 Canada National Olympiad, 3

Tags: algebra unsolved , algebra

We denote an arbitrary permutation of the integers $1$, $2$, $\ldots$, $n$ by $a_1$, $a_2$, $\ldots$, $a_n$. Let $f(n)$ denote the number of these permutations such that: (1) $a_1 = 1$; (2):$|a_i - a_{i+1}| \leq 2$, $i = 1, \ldots, n - 1$. Determine whether $f(1996)$ is divisible by 3.

2010 Germany Team Selection Test, 1

Tags: algebra unsolved , algebra

A sequence $\left(a_n\right)$ with $a_1 = 1$ satisfies the following recursion: In the decimal expansion of $a_n$ (without trailing zeros) let $k$ be the smallest digest then $a_{n+1} = a_n + 2^k.$ How many digits does $a_{9 \cdot 10^{2010}}$ have in the decimal expansion?

2008 China National Olympiad, 3

Tags: inequalities , algebra unsolved , algebra

Given a positive integer $n$ and $x_1 \leq x_2 \leq \ldots \leq x_n, y_1 \geq y_2 \geq \ldots \geq y_n$, satisfying \[\displaystyle\sum_{i = 1}^{n} ix_i = \displaystyle\sum_{i = 1}^{n} iy_i\] Show that for any real number $\alpha$, we have \[\displaystyle\sum_{i =1}^{n} x_i[i\alpha] \geq \displaystyle\sum_{i =1}^{n} y_i[i\alpha]\] Here $[\beta]$ denotes the greastest integer not larger than $\beta$.

2008 Mediterranean Mathematics Olympiad, 4

Tags: algebra , polynomial , induction , logarithms , algebra unsolved

The sequence of polynomials $(a_n)$ is defined by $a_0=0$, $ a_1=x+2$ and $a_n=a_{n-1}+3a_{n-1}a_{n-2} +a_{n-2}$ for $n>1$. (a) Show for all positive integers $k,m$: if $k$ divides $m$ then $a_k$ divides $a_m$. (b) Find all positive integers $n$ such that the sum of the roots of polynomial $a_n$ is an integer.

2011 Postal Coaching, 1

Tags: function , algebra unsolved , algebra

Let $X$ be the set of all positive real numbers. Find all functions $f : X \longrightarrow X$ such that \[f (x + y) \ge f (x) + yf (f (x))\] for all $x$ and $y$ in $X$.

1987 IMO Longlists, 50

Tags: algebra , polynomial , algebra unsolved

Let $P,Q,R$ be polynomials with real coefficients, satisfying $P^4+Q^4 = R^2$. Prove that there exist real numbers $p, q, r$ and a polynomial $S$ such that $P = pS, Q = qS$ and $R = rS^2$. [hide="Variants"]Variants. (1) $P^4 + Q^4 = R^4$; (2) $\gcd(P,Q) = 1$ ; (3) $\pm P^4 + Q^4 = R^2$ or $R^4.$[/hide]