Y by Adventure10
Let
be a triangle with circumcircle
. Let
be the midpoints of the arcs
of
containing exactly 2 points of the triangle. Let the reflections of
over
respectively be
. Let
meet
in
. Let
. Define
similarly. Prove that
concur at a point.
![[asy] /* Geogebra to Asymptote conversion, documentation at artofproblemsolving.com/Wiki, go to User:Azjps/geogebra */
import graph; size(15.46cm);
real labelscalefactor = 0.5; /* changes label-to-point distance */
pen dps = linewidth(0.7) + fontsize(10); defaultpen(dps); /* default pen style */ real xmin = -7.38, xmax = 8.08, ymin = -4.74, ymax = 4.46; /* image dimensions */
pen ttffqq = rgb(0.2,1.,0.); pen uuuuuu = rgb(0.26666666666666666,0.26666666666666666,0.26666666666666666); pen wwzzff = rgb(0.4,0.6,1.);
filldraw((-0.42,1.42)--(-0.72,-0.1)--(0.84,-0.08)--cycle, ttffqq + opacity(0.1), ttffqq);
filldraw((0.5495813513850182,-2.3473454080314182)--(2.3568579513549004,2.4621606791381163)--(-2.700193434858612,1.5421434410905153)--cycle, wwzzff + opacity(0.1), wwzzff);
/* draw figures */
draw((-0.42,1.42)--(-0.72,-0.1), ttffqq);
draw((-0.72,-0.1)--(0.84,-0.08), ttffqq);
draw((0.84,-0.08)--(-0.42,1.42), ttffqq);
draw(circle((0.05195839675291731,0.5372450532724504), 1.0010000121066647));
draw((0.5495813513850182,-2.3473454080314182)--(2.3568579513549004,2.4621606791381163), wwzzff);
draw((2.3568579513549004,2.4621606791381163)--(-2.700193434858612,1.5421434410905153), wwzzff);
draw((-2.700193434858612,1.5421434410905153)--(0.5495813513850182,-2.3473454080314182), wwzzff);
draw((-2.700193434858612,1.5421434410905153)--(1.4043043264301158,-0.07276532914833184));
draw((-1.3216922153131268,-0.1077140027604247)--(2.3568579513549004,2.4621606791381163));
draw((-1.3216922153131268,-0.1077140027604247)--(1.4043043264301158,-0.07276532914833184));
draw((-0.8112649979811452,1.8857916642632677)--(0.5495813513850182,-2.3473454080314182));
draw((1.2280103450579969,-0.5419170774499965)--(-2.700193434858612,1.5421434410905153));
draw((-0.8112649979811452,1.8857916642632677)--(1.2280103450579969,-0.5419170774499965));
draw((-0.8362044832515221,-0.6887693818077115)--(2.3568579513549004,2.4621606791381163));
draw((-0.3100711868956388,1.9769726530620972)--(0.5495813513850182,-2.3473454080314182));
draw((-0.3075640492964691,0.6007668334291895)--(0.5495813513850182,-2.3473454080314182));
draw((-0.28966430714849944,0.263266665517739)--(2.3568579513549004,2.4621606791381163));
draw((0.04666976516840058,0.18245536445196603)--(-2.700193434858612,1.5421434410905153));
draw((-0.3100711868956388,1.9769726530620972)--(-0.8362044832515221,-0.6887693818077115));
/* dots and labels */
dot((-0.42,1.42),blue);
label("$A$", (-0.56,1.66), NE * labelscalefactor,blue);
dot((-0.72,-0.1),blue);
label("$B$", (-0.62,-0.04), NE * labelscalefactor,blue);
dot((0.84,-0.08),blue);
label("$C$", (1.02,-0.32), NE * labelscalefactor,blue);
dot((0.0647906756925091,-0.46367270401570915),linewidth(3.pt) + uuuuuu);
label("$M_A$", (0.14,-0.34), NE * labelscalefactor,uuuuuu);
dot((0.8184289756774501,1.1810803395690581),linewidth(3.pt) + uuuuuu);
label("$M_B$", (0.98,0.98), NE * labelscalefactor,uuuuuu);
dot((-0.9300967174293059,0.7310717205452576),linewidth(3.pt) + uuuuuu);
label("$M_C$", (-1.14,0.92), NE * labelscalefactor,uuuuuu);
dot((0.5495813513850182,-2.3473454080314182),blue);
label("$D$", (0.7,-2.38), NE * labelscalefactor,blue);
dot((2.3568579513549004,2.4621606791381163),blue);
label("$E$", (2.44,2.66), NE * labelscalefactor,blue);
dot((-2.700193434858612,1.5421434410905153),blue);
label("$F$", (-2.62,1.74), NE * labelscalefactor,blue);
dot((-1.3216922153131268,-0.1077140027604247),linewidth(3.pt) + uuuuuu);
dot((1.4043043264301158,-0.07276532914833184),linewidth(3.pt) + uuuuuu);
dot((-0.3075640492964691,0.6007668334291895),linewidth(3.pt) + uuuuuu);
label("$X$", (-0.34,0.74), NE * labelscalefactor,uuuuuu);
dot((-0.8112649979811452,1.8857916642632677),linewidth(3.pt) + uuuuuu);
dot((1.2280103450579969,-0.5419170774499965),linewidth(3.pt) + uuuuuu);
dot((-0.28966430714849944,0.263266665517739),linewidth(3.pt) + uuuuuu);
label("$Y$", (-0.46,0.02), NE * labelscalefactor,uuuuuu);
dot((-0.3100711868956388,1.9769726530620972),linewidth(3.pt) + uuuuuu);
dot((-0.8362044832515221,-0.6887693818077115),linewidth(3.pt) + uuuuuu);
dot((0.04666976516840058,0.18245536445196603),linewidth(3.pt) + uuuuuu);
label("$Z$", (0.18,0.08), NE * labelscalefactor,uuuuuu);
clip((xmin,ymin)--(xmin,ymax)--(xmax,ymax)--(xmax,ymin)--cycle);
/* end of picture */
[/asy]](//latex.artofproblemsolving.com/f/0/c/f0cdc578926784cce3d30fb6d819adb1018da49b.png)














![[asy] /* Geogebra to Asymptote conversion, documentation at artofproblemsolving.com/Wiki, go to User:Azjps/geogebra */
import graph; size(15.46cm);
real labelscalefactor = 0.5; /* changes label-to-point distance */
pen dps = linewidth(0.7) + fontsize(10); defaultpen(dps); /* default pen style */ real xmin = -7.38, xmax = 8.08, ymin = -4.74, ymax = 4.46; /* image dimensions */
pen ttffqq = rgb(0.2,1.,0.); pen uuuuuu = rgb(0.26666666666666666,0.26666666666666666,0.26666666666666666); pen wwzzff = rgb(0.4,0.6,1.);
filldraw((-0.42,1.42)--(-0.72,-0.1)--(0.84,-0.08)--cycle, ttffqq + opacity(0.1), ttffqq);
filldraw((0.5495813513850182,-2.3473454080314182)--(2.3568579513549004,2.4621606791381163)--(-2.700193434858612,1.5421434410905153)--cycle, wwzzff + opacity(0.1), wwzzff);
/* draw figures */
draw((-0.42,1.42)--(-0.72,-0.1), ttffqq);
draw((-0.72,-0.1)--(0.84,-0.08), ttffqq);
draw((0.84,-0.08)--(-0.42,1.42), ttffqq);
draw(circle((0.05195839675291731,0.5372450532724504), 1.0010000121066647));
draw((0.5495813513850182,-2.3473454080314182)--(2.3568579513549004,2.4621606791381163), wwzzff);
draw((2.3568579513549004,2.4621606791381163)--(-2.700193434858612,1.5421434410905153), wwzzff);
draw((-2.700193434858612,1.5421434410905153)--(0.5495813513850182,-2.3473454080314182), wwzzff);
draw((-2.700193434858612,1.5421434410905153)--(1.4043043264301158,-0.07276532914833184));
draw((-1.3216922153131268,-0.1077140027604247)--(2.3568579513549004,2.4621606791381163));
draw((-1.3216922153131268,-0.1077140027604247)--(1.4043043264301158,-0.07276532914833184));
draw((-0.8112649979811452,1.8857916642632677)--(0.5495813513850182,-2.3473454080314182));
draw((1.2280103450579969,-0.5419170774499965)--(-2.700193434858612,1.5421434410905153));
draw((-0.8112649979811452,1.8857916642632677)--(1.2280103450579969,-0.5419170774499965));
draw((-0.8362044832515221,-0.6887693818077115)--(2.3568579513549004,2.4621606791381163));
draw((-0.3100711868956388,1.9769726530620972)--(0.5495813513850182,-2.3473454080314182));
draw((-0.3075640492964691,0.6007668334291895)--(0.5495813513850182,-2.3473454080314182));
draw((-0.28966430714849944,0.263266665517739)--(2.3568579513549004,2.4621606791381163));
draw((0.04666976516840058,0.18245536445196603)--(-2.700193434858612,1.5421434410905153));
draw((-0.3100711868956388,1.9769726530620972)--(-0.8362044832515221,-0.6887693818077115));
/* dots and labels */
dot((-0.42,1.42),blue);
label("$A$", (-0.56,1.66), NE * labelscalefactor,blue);
dot((-0.72,-0.1),blue);
label("$B$", (-0.62,-0.04), NE * labelscalefactor,blue);
dot((0.84,-0.08),blue);
label("$C$", (1.02,-0.32), NE * labelscalefactor,blue);
dot((0.0647906756925091,-0.46367270401570915),linewidth(3.pt) + uuuuuu);
label("$M_A$", (0.14,-0.34), NE * labelscalefactor,uuuuuu);
dot((0.8184289756774501,1.1810803395690581),linewidth(3.pt) + uuuuuu);
label("$M_B$", (0.98,0.98), NE * labelscalefactor,uuuuuu);
dot((-0.9300967174293059,0.7310717205452576),linewidth(3.pt) + uuuuuu);
label("$M_C$", (-1.14,0.92), NE * labelscalefactor,uuuuuu);
dot((0.5495813513850182,-2.3473454080314182),blue);
label("$D$", (0.7,-2.38), NE * labelscalefactor,blue);
dot((2.3568579513549004,2.4621606791381163),blue);
label("$E$", (2.44,2.66), NE * labelscalefactor,blue);
dot((-2.700193434858612,1.5421434410905153),blue);
label("$F$", (-2.62,1.74), NE * labelscalefactor,blue);
dot((-1.3216922153131268,-0.1077140027604247),linewidth(3.pt) + uuuuuu);
dot((1.4043043264301158,-0.07276532914833184),linewidth(3.pt) + uuuuuu);
dot((-0.3075640492964691,0.6007668334291895),linewidth(3.pt) + uuuuuu);
label("$X$", (-0.34,0.74), NE * labelscalefactor,uuuuuu);
dot((-0.8112649979811452,1.8857916642632677),linewidth(3.pt) + uuuuuu);
dot((1.2280103450579969,-0.5419170774499965),linewidth(3.pt) + uuuuuu);
dot((-0.28966430714849944,0.263266665517739),linewidth(3.pt) + uuuuuu);
label("$Y$", (-0.46,0.02), NE * labelscalefactor,uuuuuu);
dot((-0.3100711868956388,1.9769726530620972),linewidth(3.pt) + uuuuuu);
dot((-0.8362044832515221,-0.6887693818077115),linewidth(3.pt) + uuuuuu);
dot((0.04666976516840058,0.18245536445196603),linewidth(3.pt) + uuuuuu);
label("$Z$", (0.18,0.08), NE * labelscalefactor,uuuuuu);
clip((xmin,ymin)--(xmin,ymax)--(xmax,ymax)--(xmax,ymin)--cycle);
/* end of picture */
[/asy]](http://latex.artofproblemsolving.com/f/0/c/f0cdc578926784cce3d30fb6d819adb1018da49b.png)