geometry problems from All-Ukrainian Correspodence MO for grades 5-12 (years 1996 -2016 by magazine ''In the World of Mathematics''' ) with aops links
Всеукраїнська заочна математична олімпіада
collected inside aops here
all problems in Ukrainian here
2003 - 2021
looking for 8 first rounds (1996-2002), I-VII
Let O be the center of the circle \omega, and let A be a point inside this circle, different from O. Find all points P on the circle \omega for which the angle \angle OPA acquires the greatest value.
In the triangle ABC, D is the midpoint of AB, and E is the point on the side BC, for which CE = \frac13 BC. It is known that \angle ADC =\angle BAE. Find \angle BAC.
Let ABCDEF be a convex hexagon, P, Q, R be the intersection points of AB and EF, EF and CD, CD and AB. S, T,UV are the intersection points of BC and DE, DE and FA, FA and BC, respectively. Prove that if \frac{AB}{PR}=\frac{CD}{RQ}=\frac{EF}{QP}, then \frac{BC}{US}=\frac{DE}{ST}=\frac{FA}{TU}.
6 apple trees grow in the garden. Could it be that among any three apple trees, one is at the same distance from the other two?
A circle is drawn on the plane. How to use only a ruler to draw a perpendicular from a given point outside the circle to a given line passing through the center of this circle?
The extensions of the sides AB and CD of the trapezoid ABCD intersect at point E. Denote by H and G the midpoints of BD and AC. Find the ratio of the area AEGH to the area ABCD.
In an isosceles triangle ABC (AB = AC), the bisector of the angle B intersects AC at point D such that BC = BD + AD. Find \angle A.
An equilateral triangle with side 8 is divided into equilateral triangles with side 1. What is the largest number of these triangles that can be colored so that no two colored triangles have common vertices?
The bisectors of the angles A and B of the triangle ABC intersect the sides BC and AC at points D and E. It is known that AE + BD = AB. Find the angle \angle C.
Let O be the point of intersection of the diagonals of the trapezoid ABCD with the bases AB and CD. It is known that \angle AOB = \angle DAB = 90^o. On the sides AD and BC take the points E and F so that EF\parallel AB and EF = AD. Find the angle \angle AOE.
Let the circle \omega be circumscribed around the triangle \vartriangle ABC with right angle \angle A. Tangent to the circle \omega at point A intersects the line BC at point D. Point E is symmetric to A with respect to the line BC. Let K be the foot of the perpendicular drawn from point A on BE, L the midpoint of AK. The line BL intersects the circle \omega for the second time at the point N. Prove that the line BD is tangent to the circle circumscribed around the triangle \vartriangle ADM.
Find the locus of the points of intersection of the othocenters of the triangles inscribed in a given circle.
Mark 101 points on the plane, none of which are not lie on one line and none of the four lie on the same circle. Prove that there is a circle that passes through three of these points and for which exactly 49 marked points lie inside and exactly 49 outside.
Let D and E be the midpoints of the sides BC and AC of a right triangle ABC. Prove that if \angle CAD=\angle ABE, then\frac{5}{6} \le \frac{AD}{AB}\le \frac{\sqrt{73}}{10}.
Let ABC be an isosceles triangle (AB=AC). An arbitrary point M is chosen on the extension of the BC beyond point B. Prove that the sum of the radius of the circle inscribed in the triangle AMB and the radius of the circle tangent to the side AC and the extensions of the sides AM, CM of the triangle AMC does not depend on the choice of point M.
The vertices of a regular 1000-gon are painted red, blue and yellow. In one step, you can select two adjacent vertices of different colors and repaint them with a third color. Is it always possible to get a polygon in a few such steps, all vertices of which have a common color?
Is it possible to draw a pentagon on plaid paper with the side of cell 1 so that all its vertices lie in the nodes of the grid, and the product of the lengths of all sides and the product of the lengths of all diagonals are integers?
Let ABC be an isosceles triangle (AB = AC), D be the midpoint of BC, and M be the midpoint of AD. On the segment BM take a point N such that \angle BND = 90^o. Find the angle ANC.
In triangle ABC, the lengths of all sides are integers, \angle B=2 \angle A and \angle C> 90^o. Find the smallest possible perimeter of this triangle.
Denote by B_1 and C_1, the midpoints of the sides AB and AC of the triangle ABC. Let the circles circumscribed around the triangles ABC_1 and AB_1C intersect at points A and P, and let the line AP intersect the circle circumscribed around the triangle ABC at points A and Q. Find the ratio \frac{AQ}{AP}.
Tom made two rectangles of 2 \times 6 and 7 \times 8 from several rectangular tiles measuring 1 \times 3 and 1 \times 4, but Jerry snatched and hid one tile from each of the rectangles. Will Tom be able to make a 5 \times 12 rectangle from the remaining tiles?
What is the largest n such that exists a n-gon, in which two adjacent sides have length 1, and all diagonals have integer lengths?
On the sides AC and AB of the triangle ABC, the points D and E were chosen such that \angle ABD =\angle CBD and 3 \angle ACE = 2\angle BCE. Let H be the point of intersection of BD and CE, and CD = DE = CH. Find the angles of triangle ABC.
Let ABCD be a parallelogram. A circle with diameter AC intersects line BD at points P and Q. The perpendicular on AC passing through point C, intersects lines AB and AD at points X and Y, respectively. Prove that the points P, Q, X and Y lie on the same circle.
A maze is an 8\times 8 chessboard with walls between some cells so that you can go from one cell to another. By the command "\uparrow", "\downarrow "," \rightarrow "or" \leftarrow" the hobbit, which is in one of the cells, moves one cell down, up, left or right, if it does not bump into the wall or edge of the board. Otherwise, it remains in place. Gandalf writes a program that consists only of the commands \uparrow", "\downarrow "," \rightarrow " and " \leftarrow" and passes it to Saruman, who builds a maze, selects the starting cell for the hobbit and forces him to run the program. Can Gandalf guarantee that by following his program, the hobbit will visit all the cells of the chessboard?
A right triangle is drawn on the plane. How to use only a compass to mark two points, such that the distance between them is equal to the diameter of the circle inscribed in this triangle?
Let ABCDE be a convex pentagon such that AE\parallel BC and \angle ADE = \angle BDC. The diagonals AC and BE intersect at point F. Prove that \angle CBD= \angle ADF.
The equilateral triangle ABC is divided into 100 equal equilateral triangles. Is it possible to mark 8 vertices of small triangles so that no segment with ends at the marked points is parallel to any side of triangle ABC?
In triangle ABC, the length of the angle bisector AD is \sqrt{BD \cdot CD}. Find the angles of the triangle ABC, if \angle ADB = 45^o.
Prove that for every n\ge 4 there is a hexagon that can be cut into n identical triangles.
An arbitrary point D was marked on the median BM of the triangle ABC. It is known that the point DE\parallel AB and CE \parallel BM. Prove that BE = AD
Let ABC be an acute-angled triangle in which \angle BAC = 60^o and AB> AC. Let H and I denote the points of intersection of the altitudes and angle bisectors of this triangle, respectively. Find the ratio \angle ABC: \angle AHI.
The kid cut out of grid paper with the side of the cell 1 rectangle along the grid lines and calculated its area and perimeter. Carlson snatched his scissors and cut out of this rectangle along the lines of the grid a square adjacent to the boundary of the rectangle.
- My rectangle ... - kid sobbed. - There is something strange about this figure!
- Nonsense, do not mention it - Carlson said - waving his hand carelessly. - Here you see, in this figure the perimeter is the same as the area of the rectangle was, and the area is the same as was the perimeter!
What size square did Carlson cut out?
Let ABCD be a trapezoid in which AB \parallel CD and AB = 2CD. A line \ell perpendicular to CD was drawn through point C. A circle with center at point D and radius DA intersects line \ell at points P and Q. Prove that AP \perp BQ.
On the diagonals AC and CE of a regular hexagon ABCDEF with side 1 we mark points M and N such that AM = CN = a. Find a if the points B, M, N lie on the same line.
In a quadrilateral ABCD, the diagonals are perpendicular and intersect at the point S. Let K, L, M, and N be points symmetric to S with respect to the lines AB, BC, CD, and DA, respectively, BN intersects the circumcircle of the triangle SKN at point E, and BM intersects described the circle of the triangle SLM at the point F. Prove that the quadrilateral EFLK is cyclic .
Can a square be cut into a triangle, quadrilateral, pentagon, and hexagon (not necessarily convex) such that none of these polygons has right angles?
Beetles sit on the nodes of the 3 \times 100 grid (100 beetles in each row and 3 beetles in each column). How many straight lines can be drawn on which exactly 3 beetles sit?
Let O and H be the center of the circumcircle and the point of intersection of the altitudes of the acute triangle ABC respectively, D be the foot of the altitude drawn to BC, and E be the midpoint of AO. Prove that the circumcircle of the triangle ADE passes through the midpoint of the segment OH.
The diagonals AC and BD of the cyclic quadrilateral ABCD intersect at a point O. It is known that \angle BAD = 60^o and AO = 3OC. Prove that the sum of some two sides of a quadrilateral is equal to the sum of the other two sides.
An arbitrary point D is marked on the hypotenuse AB of a right triangle ABC. The circle circumscribed around the triangle ACD intersects the line BC at the point E for the second time, and the circle circumscribed around the triangle BCD intersects the line AC for the second time at the point F. Prove that the line EF passes through the point D.
Given 11 rectangles of different sizes, all sides of which are integral and do not exceed 10. Prove that there are three of these rectangles, that the first can be placed inside the second, and the second can be placed inside the third.
Let E be the point of intersection of the diagonals of the cyclic quadrilateral ABCD, and let K, L, M and N be the midpoints of the sides AB, BC, CD and DA, respectively. Prove that the radii of the circles circumscribed around the triangles KLE and MNE are equal.
Given a triangle ABC. The circle \omega_1 passes through the vertex B and touches the side AC at the point A, and the circle \omega_2 passes through the vertex C and touches the side AB at the point A. The circles \omega_1 and \omega_2 intersect a second time at the point D. The line AD intersects the circumcircle of the triangle ABC at point E. Prove that D is the midpoint of AE.
Krut and Vert go by car from point A to point B. The car leaves A in the direction of B, but every 3 km of the road Krut turns 90^o to the left, and every 7 km of the road Vert turns 90^o to the right ( if they try to turn at the same time, the car continues to go in the same direction). Will Krut and Vert be able to get to B if the distance between A and B is 100 km?
Is it possible to cut a rectangle with sides 1 and 4 into four parts and fold of them a new rectangle in which one side is twice as long as the other?
Let ABC be an isosceles triangle (AB = AC). The points D and E were marked on the ray AC so that AC = 2AD and AE = 2AC. Prove that BC is the bisector of the angle \angle DBE.
In the triangle ABC, it is known that AC <AB. Let \ell be tangent to the circumcircle of triangle ABC drawn at point A. A circle with center A and radius AC intersects segment AB at point D, and line \ell at points E and F. Prove that one of the lines DE and DF passes through the center inscribed circle of triangle ABC.
Let \omega be the circumscribed circle of triangle ABC, and let \omega' 'be the circle tangent to the side BC and the extensions of the sides AB and AC. The common tangents to the circles \omega and \omega' intersect the line BC at points D and E. Prove that \angle BAD = \angle CAE.
Is it possible to place four triangles on the plane so that inside each triangle was exactly one vertex of the other three triangles?
On the sides BC, AC and AB of the equilateral triangle ABC mark the points D, E and F so that \angle AEF = \angle FDB and \angle AFE = \angle EDC. Prove that DA is the bisector of the angle EDF.
Let ABC be an non- isosceles triangle, H_a, H_b, and H_c be the feet of the altitudes drawn from the vertices A, B, and C, respectively, and M_a, M_b, and M_c be the midpoints of the sides BC, CA, and AB, respectively. The circumscribed circles of triangles AH_bH_c and AM_bM_c intersect for second time at point A'. The circumscribed circles of triangles BH_cH_a and BM_cM_a intersect for second time at point B'. The circumscribed circles of triangles CH_aH_b and CM_aM_b intersect for second time at point C'. Prove that points A', B' and C' lie on the same line.
We say that two triangles are [i]similar[/i] if they are both acute, both right, or both obtuse. In the
vertices of a regular n-gon (n\ge 3) sat n sparrows, one in each vertex. Then they flew into the
air and again sat on the vertices of this n-gon, one at each vertex, but possibly in a different order.
Which n is sure to find three sparrows that sat in the vertices of similar triangles before and after the
flight?
Four congurent triangles are placed on the plane so that every two triangles have two common vertices. Will there be a vertex that is common to all four triangles?
In some cells of the table n x n, n\ge 2 there are sitting fireflies. Each firefly illuminates all the cells of the row and column in which it is located (including the cell in which it sits). In each cell of the table recorded the number of fireflies that illuminate it. At which n can it happen that the numbers on each of the diagonals are not repeated?
The circle \omega inscribed in an isosceles triangle ABC (AC = BC) touches the side BC at point D .On the extensions of the segment AB beyond points A and B, respectively mark the points K and L so that AK = BL, The lines KD and LD intersect the circle \omega for second time at points G and H, respectively. Prove that point A belongs to the line GH.
A triangle, a line and three rectangles are located on a plane so that one of the sides of each rectangle is parallel to this line and the rectangles completely cover all sides of the triangle. Prove that the rectangles cover the whole triangle.
Inside the square ABCD mark the point P, for which \angle BAP = 30^o and \angle BCP = 15^o. The point Q was chosen so that APCQ is an isosceles trapezoid (PC\parallel AQ). Find the angles of the triangle CAM, where M is the midpoint of PQ.
A 5 \times 12 chocolate bar consists of 30 black and 30 pieces of milk (not necessarily arranged in a checkerboard pattern). Can any such tile be broken into three rectangles so that either each rectangle has an even number of black pieces, or each rectangle has an even number of milk pieces?
On the midline of the isosceles trapezoid ABCD (BC \parallel AD) find the point K, for which the sum of the angles \angle DAK + \angle BCK will be the smallest.
Inside the parallelogram ABCD, choose a point P such that \angle APB+ \angle CPD= \angle BPC+ \angle APD. Prove that there exists a circle tangent to each of the circles circumscribed around the triangles APB, BPC, CPD and APD.
A rectangle of size 5x11 was cut along the cell lines into two identical shapes, from which you can make a square, and a number of individual cells. What is the smallest number of individual cells that could be formed?
Let AD and AE be the altitude and median of triangle ABC, in with \angle B = 2\angle C. Prove that AB = 2DE.
Let ABC be an acute-angled triangle in which AB <AC. On the side BC mark a point D such that AD = AB, and on the side AB mark a point E such that the segment DE passes through the orthocenter of triangle ABC. Prove that the center of the circumcircle of triangle ADE lies on the segment AC.
Is it possible to place on a plane 5 circles of radius 12 and 12 circles of radius 5 so that each small circle touches one small and two large circles?
Given a triangle ABC. Construct a point D on the side AB and point E on the side AC so that BD = CE and \angle ADC = \angle BEC
The symbol of the Olympiad shows 5 regular hexagons with side a, located inside a regular hexagon with side b. Find ratio \frac{a}{b}.
A rectangle was cut into smaller rectangles by horizontal and vertical lines so that there was at least one horizontal and at least one vertical section. It turned out that the areas of all formed rectangles form an arithmetic progression. Prove that all these rectangles are equal.
Let O be the center of the circle circumscribed around the acute triangle ABC, and let N be the midpoint of the arc ABC of this circle. On the sides AB and BC mark points D and E respectively, such that the point O lies on the segment DE. The lines DN and BC intersect at the point P, and the lines EN and AB intersect at the point Q. Prove that PQ \perp AC.
A square and several straight lines that do not pass through its vertices are drawn on the plane. For each side and each diagonal of the square, calculate the number of lines that intersect this segment. Could it be that these numbers are six consecutive natural numbers?
Let ABC be an acute triangle, D be the midpoint of BC. Bisectors of angles ADB and ADC intersect the circles circumscribed around the triangles ADB and ADC at points E and F, respectively. Prove that EF\perp AD.
The diagonals of the cyclic quadrilateral ABCD intersect at the point E. Let P and Q are the centers of the circles circumscribed around the triangles BCE and DCE, respectively. A straight line passing through the point P parallel to AB, and a straight line passing through the point Q parallel to AD, intersect at the point R. Prove that the point R lies on segment AC.
Let I be the center of a circle inscribed in triangle ABC, in which \angle BAC = 60 ^o and AB \ne AC. The points D and E were marked on the rays BA and CA so that BD = CE = BC. Prove that the line DE passes through the point I.
Let D be a point on the side AB of the triangle ABC such that BD = CD, and let the points E on the side BC and F on the extension AC beyond the point C be such that EF\parallel CD. The lines AE and CD intersect at the point G. Prove that BC is the bisector of the angle FBG.
details of issues of magazine ''У світі математики'' that were posted the missing correspondece MOs:
2003 /9/4 VIII Всеукраїнська заочна математична олімпіада
2002 /8/4 VII Всеукраїнська заочна математична олімпіада
2001 /7/4 VI Всеукраїнська заочна математична олімпіада
2000 /6/4 V Всеукраїнська заочна математична олімпіада
1999 /?? IV Всеукраїнська заочна математична олімпіада
1998 /4/3 (III) Третя Всеукраїнська заочна олімпіада
1997 /3/4 (II) Заочна математична олімпіада журналу “У світі математики”
1996 /2/4 (I) Заочна математична олімпіада журналу “У світі математики”
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