Τετάρτη 18 Ιανουαρίου 2012

▪ Vietnam Pre - Vietnam Mathematical Olympiad 2012

ΗΜΕΡΑ 1η
1. For prove that
.
2. Compute
  .
3. Let be a triangle with height . lies on the circle over 3 midpoint of    (). 
Σημαία
Prove that the line connect 2 center of and go through a fixed point. (where be a circumscribed circle of triangle ).
4 Two people A and B play a game in the grid (). Each person respectively (A plays first) draw a segment between two point of the grid such that this segment doesn't contain any point (except the 2 ends) and also the segment (except the 2 ends) doesn't intersect with any other segments. The last person who can't draw is the loser. Which one (of A and B) have the winning tactics?
ΗΜΕΡΑ 2η
1. Let be a positive integer. Suppose there exist non-negative integers such that . Prove that .
2. Let defined by: , . Knowing that
(i) .
(ii) . Prove that  
3. In a country, there are some cities and the city named Ben Song is capital. Each cities are connected with others by some two-way roads. One day, the King want to choose cities to add up with Ben Song city to establish an expanded capital such that the two following condition are satisfied:
(i) With every two cities in expanded capital, we can always find a road connecting them and this road just belongs to the cities of expanded capital.
(ii) There are exactly cities which do not belong to expanded capital have the direct road to at least one city of expanded capital.
Prove that there are at most options to expand the capital for the King.

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