Difference between revisions of "2006 Romanian NMO Problems"
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''Dan Schwarz'' | ''Dan Schwarz'' | ||
− | [[2006 Romanian NMO Problems/Grade | + | [[2006 Romanian NMO Problems/Grade 9/Problem 1 | Solution]] |
===Problem 2=== | ===Problem 2=== | ||
Let <math>\displaystyle ABC</math> and <math>\displaystyle DBC</math> be isosceles triangle with the base <math>\displaystyle BC</math>. We know that <math>\displaystyle \angle ABD = \frac{\pi}{2}</math>. Let <math>\displaystyle M</math> be the midpoint of <math>\displaystyle BC</math>. The points <math>\displaystyle E,F,P</math> are chosen such that <math>\displaystyle E \in (AB)</math>, <math>\displaystyle P \in (MC)</math>, <math>\displaystyle C \in (AF)</math>, and <math>\displaystyle \angle BDE = \angle ADP = \angle CDF</math>. Prove that <math>\displaystyle P</math> is the midpoint of <math>\displaystyle EF</math> and <math>\displaystyle DP \perp EF</math>. | Let <math>\displaystyle ABC</math> and <math>\displaystyle DBC</math> be isosceles triangle with the base <math>\displaystyle BC</math>. We know that <math>\displaystyle \angle ABD = \frac{\pi}{2}</math>. Let <math>\displaystyle M</math> be the midpoint of <math>\displaystyle BC</math>. The points <math>\displaystyle E,F,P</math> are chosen such that <math>\displaystyle E \in (AB)</math>, <math>\displaystyle P \in (MC)</math>, <math>\displaystyle C \in (AF)</math>, and <math>\displaystyle \angle BDE = \angle ADP = \angle CDF</math>. Prove that <math>\displaystyle P</math> is the midpoint of <math>\displaystyle EF</math> and <math>\displaystyle DP \perp EF</math>. | ||
− | [[2006 Romanian NMO Problems/Grade | + | [[2006 Romanian NMO Problems/Grade 9/Problem 2 | Solution]] |
===Problem 3=== | ===Problem 3=== | ||
We have a quadrilateral <math>ABCD</math> inscribed in a circle of radius <math>r</math>, for which there is a point <math>P</math> on <math>CD</math> such that <math>CB=BP=PA=AB</math>. | We have a quadrilateral <math>ABCD</math> inscribed in a circle of radius <math>r</math>, for which there is a point <math>P</math> on <math>CD</math> such that <math>CB=BP=PA=AB</math>. | ||
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''Virgil Nicula'' | ''Virgil Nicula'' | ||
− | [[2006 Romanian NMO Problems/Grade | + | [[2006 Romanian NMO Problems/Grade 9/Problem 3 | Solution]] |
===Problem 4=== | ===Problem 4=== | ||
<math>\displaystyle 2n</math> students <math>\displaystyle (n \geq 5)</math> participated at table tennis contest, which took <math>\displaystyle 4</math> days. In every day, every student played a match. (It is possible that the same pair meets twice or more times, in different days) Prove that it is possible that the contest ends like this: | <math>\displaystyle 2n</math> students <math>\displaystyle (n \geq 5)</math> participated at table tennis contest, which took <math>\displaystyle 4</math> days. In every day, every student played a match. (It is possible that the same pair meets twice or more times, in different days) Prove that it is possible that the contest ends like this: | ||
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How many students won only a single match and how many won exactly <math>\displaystyle 2</math> matches? (In the above conditions) | How many students won only a single match and how many won exactly <math>\displaystyle 2</math> matches? (In the above conditions) | ||
− | [[2006 Romanian NMO Problems/Grade | + | [[2006 Romanian NMO Problems/Grade 9/Problem 4 | Solution]] |
Revision as of 09:11, 28 July 2006
Contents
7th Grade
Problem 1
Let be a triangle and the points and on the sides respectively , such that . Let be a point on the line . Prove that the lines and are perpendicular if and only if is the interior angle bisector of .
Problem 2
A square of side is formed from unit squares, each colored in red, yellow or green. Find minimal , such that for each coloring, there exists a line and a column with at least 3 unit squares of the same color (on the same line or column).
Problem 3
In the acute-angle triangle we have . The points and are the feet of the altitudes from and , and is the orthocenter of the triangle. We consider the points and on the segments and such that . Prove that
a) ;
b) .
Problem 4
Let be a set of positive integers with at least 2 elements. It is given that for any numbers , we have , where by we have denoted the least common multiple of and . Prove that the set has exactly two elements.
Marius Gherghu, Slatina
8th Grade
Problem 1
We consider a prism with 6 faces, 5 of which are circumscriptible quadrilaterals. Prove that all the faces of the prism are circumscriptible quadrilaterals.
Problem 2
Let be a positive integer. Prove that there exists an integer , , and numbers , such that
Problem 3
Let be a cube and a variable point on the side . The perpendicular plane on which passes through intersects the line in . Let and be the midpoints of the segments and respectively.
a) Prove that the lines and are perpendicular if and only if is the midpoint of .
b) Find the minimal value of the angle between the lines and .
Problem 4
Let . Prove that
selected by Mircea Lascu
Grade 9
Problem 1
Find the maximal value of
where , .
Dan Schwarz
Problem 2
Let and be isosceles triangle with the base . We know that . Let be the midpoint of . The points are chosen such that , , , and . Prove that is the midpoint of and .
Problem 3
We have a quadrilateral inscribed in a circle of radius , for which there is a point on such that .
(a) Prove that there are points which fulfill the above conditions.
(b) Prove that .
Virgil Nicula
Problem 4
students participated at table tennis contest, which took days. In every day, every student played a match. (It is possible that the same pair meets twice or more times, in different days) Prove that it is possible that the contest ends like this:
- there is only one winner;
- there are students on the second place;
- no student lost all matches.
How many students won only a single match and how many won exactly matches? (In the above conditions)