Τετάρτη 4 Μαΐου 2011

▪ Iran National Math Olympiad (Second Round) 2011

1η Ημέρα
1. We have a line and points around it such that the distance of each point to the line is less than centimeters and the distance between any two points is more than centimeters. prove that there are two points such that their distance is at least meters.
2. In triangle , we have . perpendicular line from to side intersects angle bisector of in and perpendicular line from to side intersects angle bisector of in . prove that .
3. Find all increasing sequences of natural numbers such that for each , number of the divisors of and is equal. (an increasing sequence is a sequence that if , then .)
                         
2η Ημέρα
1. find the smallest natural number such that there exists real numbers in the interval such that their sum equals zero and the sum of their squares equals .
2. rainbow is the name of a bird. this bird has colors and it's colors in two consecutive days are not equal. there doesn't exist days in this bird's life like such that and the bird has the same color in days and and the same color in days and different from the colors it has in days and . what is the maximum number of days rainbow can live in terms of ?
3. the line intersects the extension of in ( is nearer to than ) and the extension of in ( is nearer to than ) of triangle . suppose that reflection of line to perpendicular bisector of side intersects the mentioned extensions in and respectively.prove that if , then .

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