### IMAR 2003-17 (Romania) 12p (-02,04)

geometry problems from IMAR Mathematical Competition (Romanian)

2003 - 2017
missing 2002 and 2004

2002 IMAR P (missing)

2003 IMAR P
The exinscribed circle of a triangle $ABC$ corresponding to its vertex $A$ touches the sidelines $AB$ and $AC$ in the points $M$ and $P$, respectively, and touches its side $BC$ in the point $N$. Show that if the midpoint of the segment $MP$ lies on the circumcircle of triangle $ABC$, then the points $O$, $N$, $I$ are collinear, where $I$ is the incenter and $O$ is the circumcenter of triangle $ABC$.

2004 IMAR P (missing)

2005 IMAR P1
The incircle of triangle $ABC$ touches the sides $BC,CA,AB$ at the points $D,E,F$, respectively. Let $K$ be a point on the side $BC$ and let $M$ be the point on the line segment $AK$ such that $AM=AE=AF$. Denote by $L,N$ the incenters of triangles $ABK,ACK$, respectively. Prove that $K$ is the foot of the altitude from $A$ if and only if $DLMN$ is a square.

2006 IMAR P3
Consider the isosceles triangle $ABC$ with $AB = AC$, and $M$ the midpoint of $BC$. Find the locus of the points $P$ interior to the triangle, for which $\angle BPM+\angle CPA = \pi$.

2008 IMAR P3
Two circles $\gamma_{1}$ and $\gamma_{2}$ meet at points $X$ and $Y$. Consider the parallel through $Y$ to the nearest common tangent of the circles. This parallel meets again $\gamma_{1}$ and $\gamma_{2}$ at $A$, and $B$ respectively. Let $O$ be the center of the circle tangent to $\gamma_{1},\gamma_{2}$ and the circle $AXB$, situated outside $\gamma_{1}$ and $\gamma_{2}$ and inside the circle $AXB.$ Prove that $XO$ is the bisector line of the angle $\angle{AXB}.$

Consider a convex quadrilateral $ABCD$ with $AB=CB$ and $\angle ABC +2 \angle CDA = \pi$ and let $E$ be the midpoint of $AC$. Show that $\angle CDE =\angle BDA$.

Paolo Leonetti
2010 IMAR P2
Given a triangle $ABC$, let $D$ be the point where the incircle of the triangle $ABC$ touches the side $BC$. A circle through the vertices $B$ and $C$ is tangent to the incircle of triangle $ABC$ at the point $E$. Show that the line $DE$ passes through the excentre of triangle $ABC$ corresponding to vertex $A$.

2011 IMAR P1
Let $A_0A_1A_2$ be a triangle and let $P$ be a point in the plane, not situated on the circle $A_0A_1A_2$. The line $PA_k$ meets again the circle $A_0A_1A_2$ at point $B_k, k = 0, 1, 2$. A line $\ell$ through the point $P$ meets the line $A_{k+1}A_{k+2}$ at point $C_k, k = 0, 1, 2$. Show that the lines $B_kC_k, k = 0, 1, 2$, are concurrent and determine the locus of their concurrency point as the line $\ell$ turns about the point $P$.

Given a triangle $ABC$, let $D$ be a point different from $A$ on the external bisectrix $\ell$ of the angle $BAC$, and let $E$ be an interior point of the segment $AD$. Reflect $\ell$ in the internal bisectrices of the angles $BDC$ and $BEC$ to obtain two lines that meet at some point $F$. Show that the angles $ABD$ and $EBF$ are congruent.

2013 IMAR P4
Given a triangle $ABC$ , a circle centered at some point $O$ meets the segments $BC$ , $CA$ , $AB$ in the pairs of points $X$ and $X^{'}$ , $Y$ and $Y^{'}$ , $Z$ and $Z^{'}$ , respectively ,labelled in circular order : $X,X^{'},Y,Y^{'},Z,Z^{'}$. Let $M$ be the Miquel point of the triangle $XYZ$ and let $M^{'}$ be that of the triangle $X^{'}Y^{'}Z^{'}$ . Prove that the segments $OM$ and $OM^{'}$ have equal lehgths.

Let $ABC$ be a triangle and let $M$ be the midpoint of the side $BC$ . The circle with radius $MA$ centered in $M$ meets the lines $AB$ and $AC$ again at $B^{'}$ and $C^{'}$, respectively , and the tangents to this circle at $B^{'}$ and $C^{'}$ meet at $D$ . Show that the perpendicular bisector of the segment $BC$ bisects the segment $AD$.

2015 IMAR P3
Let $ABC$ be a triangle, let $A_1, B_1, C_1$ be the antipodes of the vertices $A, B, C$, respectively, in the circle $ABC$, and let $X$ be a point in the plane $ABC$, collinear with no two vertices of the triangle $ABC$. The line through $B$, perpendicular to the line $XB$, and the line through $C$, perpendicular to the line $XC$, meet at $A_2$, the points $B_2$ and $C_2$ are defined similarly. Show that the lines $A_1A_2, B_1B_2$ and $C_1C_2$ are concurrent.

2017 IMAR P1
Let $P$ be a point in the interior $\triangle ABC$, and $AD,BE,CF$ 3 concurrent cevians through $P$, with $D,E,F$ on $BC,CA,AB$. The circle with the diameter $BC$ intersects the circle with the diameter $AD$ in $D_1,D_2$. Analogously we define $E_1,E_2$ and $F_1,F_2$. Prove that $D_1,D_2,E_1,E_2,F_1,F_2$ are concylic.