IMO 1976

Official IMO 1976 problems  ·  6/6 solved, 1 verified.

Problem 1   solved · 4m06s · Solution →

In a convex quadrilateral (in the plane) with the area of $32 \text{ cm}^{2}$ the sum of two opposite sides and a diagonal is $16 \text{ cm}$. Determine all the possible values that the other diagonal can have.

Problem 2   solved · 4m04s · Solution →

Let $P_{1}(x) = x^{2} - 2$ and $P_{j}(x) = P_{1}(P_{j - 1}(x))$ for $j= 2,\ldots$ Prove that for any positive integer n the roots of the equation $P_{n}(x) = x$ are all real and distinct.

Problem 3   solved · 4m11s · Solution →

A box whose shape is a parallelepiped can be completely filled with cubes of side $1.$ If we put in it the maximum possible number of cubes, each of volume $2$, with the sides parallel to those of the box, then exactly $40$ percent from the volume of the box is occupied. Determine the possible dimensions of the box.

Problem 4   ✓ verified · 5m33s · Solution →

Find the largest number obtainable as the product of positive integers whose sum is $1976$.

Problem 5   solved · 5m25s · Solution →

Let a set of $p$ equations be given, $$ \begin{array}{ccccccc} a_{11}x_1&+&\cdots&+&a_{1q}x_q&=&0,\ a_{21}x_1&+&\cdots&+&a_{2q}x_q&=&0,\ &&&\vdots&&&\ a_{p1}x_1&+&\cdots&+&a_{pq}x_q&=&0,\ \end{array} $$ with coefficients $a_{ij}$ satisfying $a_{ij}=-1$, $0$, or $+1$ for all $i=1,\dots, p$, and $j=1,\dots, q$. Prove that if $q=2p$, there exists a solution $x_1, \dots, x_q$ of this system such that all $x_j$ ($j=1,\dots, q$) are integers satisfying $|x_j|\le q$ and $x_j\ne 0$ for at least one value of $j$.

Problem 6   solved · 7m15s · Solution →

For all positive integral $n$, $u_{n+1}=u_n(u_{n-1}^2-2)-u_1$, $u_0=2$, and $u_1=2\frac12$. Prove that $$ 3\log_2[u_n]=2^n-(-1)^n, $$ where $[x]$ is the integral part of $x$.