L153. Găsiţi toate funcţiile f : R → R cu proprietatea căf ¡ x 2 + xy + yf (y) ¢ = xf (x + y)+f 2 (y) , ∀x, y ∈ R.Adrian Zahariuc, student, PrincetonL154. Fie P ∈ R [X] un polinom de gradul n şi p : R → R funcţia polinomialăasociată. Ştiind că mulţimea {x ∈ R | p (x) =0} are k elemente (distincte), iarfuncţia f : R → R, f (x) =|p (x)| este derivabilă peR, h arătaţi că numărul maxim denirădăcini complexe nenule ale lui P este egal cu 2 − 2k.2Vlad Emanuel, student, BucureştiL155. Fie A, B ∈ M 2 (C) două matrice astfel încât matricea AB − BA să fieinversabilă. Să searatecă urma matricei (I 2 + AB)(AB − BA) −1 este egală cu1.Florina Cârlan şi Marian Tetiva, BârladTraining problems for mathematical contestsA. Junior highschool levelG146. Let x, y, z ∈ (0, ∞) such that xyz =1.Provethatxy 3x 4 + y + z + yz 3y 4 + z + x + zx 3z 4 + x + y ≥ 1.Liviu Smarandache and Lucian Tuţescu, CraiovaG147. Let n ∈ N, n ≥ 2 be a fixed number and let a, b, c be natural numbersh n − 1isuch that na +(n +1)b +2nc = n 2 +1. Show that n − ≤ a + b + c ≤ n.2Gheorghe Iurea, IaşiG148. Let a 1 a 2 ...a p ∈ N. Show that every natural number has a multiple ofthe form a 1 a 2 ...a p a 1 a 2 ...a p ...a 1 a 2 ...a p 0 ...0.Marian Panţiruc, IaşiG149. a) Determine two prime numbers p, q so that p
) Show that we cannot find a numbering for the upper basis so that i + a. i 9,∀i ∈ {1, 2,...,2008}.Gabriel Popa and Gheorghe Iurea, IaşiG152. In the isosceles triangle ABC (AB = AC), B 0 , C 0 denote the feet ofthe altitudes from B, respectively C. If AB =2B 0 C 0 , determine the angles of thetriangle.Nela Ciceu, BacăuandTituZvonaru,ComăneştiG153. In the triangle ABC, M is the midpoint of the side [BC], m(\ABC) =30 ◦and m(\ACB) = 105 ◦ . The perpendicular from C on AM cuts AB at Q. Calculatrethe value of the ratio QAQB .Neculai Roman, Mirceşti (Iaşi)G154. Let D be the midpoint of the side [BC] in the equilateral triangle ABCof side length 1, andletP beamovingpointon[CD]. Denote by M and N theprojections of the points B, respectively C on AP Find the area of the geometriclocus described by the segment [MN].Mariu Olteanu, Rm. VâlceaG155. Let C be the circumcircle of the acute-angled triangle 4ABC. DenotebyP the intersection point of the tangents to the circle at B and C, {D} = AP ∩ C,while M and N are the midpoints of the small arc BC, respectively of the big arcBC. Show that the straight lines AM, DN and BC meet at a point.Gabriel Popa, IaşiB. Highschool levelL146. The straight lines d 1 , d 2 ,..., d n+1 , are considered in the plane such thatany two lines are not parallel. We denote by α k = m( d k\,d k+1 ), α k ≤ 90 ◦ , k = 1,n.Asegmentoflength2 is cosidered on d 1 that is projected on d 2 , then the obtainedsegment is projected on d 3 and so on, until a segment of length 1 is obtained ond n+1 . Knowing that tan ¡ min © α i | i = 1,n ª¢ = p √ n4 − 1, determine the angles α k ,k = 1,n.Cristian Săvescu, student, BucureştiL147. A convex polygon with n sides, n ≥ 4, isconsideredsuchthatanypairofdiagonals are not parallel and and any three diagonals do not meet at other pointsexcept the vertices of the polygon. Let us denote by n i the number of intersectionpoints of the diagonals inside the polygon and by n e the number of intersection pointsof the diagonals outside the polygon.a) Show that exactly eight polygons exist such that the inequality n i >n e issatisfied.b) Show that exactly three polygons exist such that n i + n e kn 2 , k ∈ N ∗ .Mihai Haivas, IaşiL148. ApointD is considered on the side (AB) of the triangle ABC such thatAB =4AD. In the same halfplane as point C with respect to the side AB, wetakeapointP such that \PDA ≡ \ACB and PB =2PD. Prove that the quadrilateralABCP is inscriptible, that si it admits a circumscribed circle.Nela Ciceu, BacăuandTituZvonaru,Comăneşti179
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Anul X, Nr. 2Iulie - Decembrie 2008
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A colaborat la elaborarea unui trat
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pământ primele capitole elevate d
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de "Gazeta Matematică".La 125 de a
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calendarul iudaic). De la data Conc
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mecanic virtual".CursulluiM.Tzony(
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Câteva probleme de teoria numerelo
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Soluţie. De astă dată, pe lâng
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Se demonstrează imediatcă H 1 H 2
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În scopul propus, să notăm x n =
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Cercuri semiînscriseşi puncte de
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O rafinare a inegalităţii lui Jen
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Asupra unor inegalităţi geometric
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Grupând convenabil, obţinem(3ab +
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