Circum circles of subtriangles: Difference between revisions
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Let ABC be a triangle and let the incircle intersect BC, CA, and AB at A', B', and C', respectively. | Let ABC be a triangle and let the incircle intersect <math>BC</math>, <math>CA</math>, and <math>AB</math> at <math>A'</math>, <math>B'</math>, and <math>C'</math>, respectively. | ||
Let the circumcircles of AB'C', A'BC', and A'B'C intersect the circumcircle of ABC (apart from A, B, and C) at A'', B'', and C'', respectively. | Let the circumcircles of <math>AB'C'</math>, <math>A'BC'</math>, and <math>A'B'C</math> intersect the circumcircle of <math>ABC</math> (apart from <math>A</math>, <math>B</math>, and <math>C</math>) at <math>A''</math>, <math>B''</math>, and <math>C''</math>, respectively. | ||
Then A'A'', B'B'', and C'C'' meet in one point, P. | Then <math>A'A''</math>, <math>B'B''</math>, and <math>C'C''</math> meet in one point, <math>P</math>. | ||
<jsxgraph width="800" height="600"> | <jsxgraph width="800" height="600"> | ||
brd = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-1,4,12,-4], keepaspectratio:true}); | brd = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-1,4,12,-4], keepaspectratio:true}); | ||
p1 = brd. | p1 = brd.create('point', [0.5,-1.5] , {name:'A',fillColor:'red',strokeColor:'red'}); | ||
p2 = brd. | p2 = brd.create('point', [7.5,0.5] , {name:'B',fillColor:'red',strokeColor:'red'}); | ||
p3 = brd. | p3 = brd.create('point', [2,3] , {name:'C',fillColor:'red',strokeColor:'red'}); | ||
b1 = brd. | b1 = brd.create('segment',['A','B'],{name:''}); | ||
b2 = brd. | b2 = brd.create('segment',['A','C'],{name:''}); | ||
b3 = brd. | b3 = brd.create('segment',['C','B'],{name:''}); | ||
c1 = brd. | c1 = brd.create('circumcircle',['A','B','C'],{name:'', point: {visible: false}}); | ||
c1 | c1.setProperty('strokeColor:#AAAAAA'); | ||
l1 = brd. | l1 = brd.create('bisector',['B','A','C'],{name:'',visible:false}); // alpha | ||
l2 = brd. | l2 = brd.create('bisector',['C','B','A'],{name:'',visible:false}); // beta | ||
i1 = brd. | i1 = brd.create('intersection',[l1,l2,0],{name:'',visible:false}); | ||
pp1 = brd. | pp1 = brd.create('perpendicularpoint',[i1,b1],{name:"C'",fillColor:'blue'}); | ||
pp2 = brd. | pp2 = brd.create('perpendicularpoint',[i1,b2],{name:"B'",fillColor:'blue'}); | ||
pp3 = brd. | pp3 = brd.create('perpendicularpoint',[i1,b3],{name:"A'",fillColor:'blue'}); | ||
c2 = brd. | c2 = brd.create('circumcircle',[pp1,pp2,pp3],{name:'', strokeColor: '#3CB371', point: {visible: false}}); | ||
c3 = brd.create('circumcircle',[p3,pp2,pp3],{name:'', strokeColor: '#FF8C00', point: {visible: false}}); | |||
c4 = brd.create('circumcircle',[p2,pp1,pp3],{name:'', strokeColor: '#FF8C00', point: {visible: false}}); | |||
c5 = brd.create('circumcircle',[p1,pp2,pp1],{name:'', strokeColor: '#FF8C00', point: {visible: false}}); | |||
i2 = brd.create('otherintersection',[c3,c1,p3],{name:"C''",fillColor:'blue'}); | |||
i3 = brd.create('otherintersection',[c4,c1,p2],{name:"B''",fillColor:'blue'}); | |||
i4 = brd.create('otherintersection',[c5,c1,p1],{name:"A''",fillColor:'blue'}); | |||
ll1 = brd.create('segment',[i2,pp1],{name:'',strokeColor:'#FF6347'}); | |||
ll2 = brd.create('segment',[i3,pp2],{name:'',strokeColor:'#FF6347'}); | |||
ll3 = brd.create('segment',[i4,pp3],{name:'',strokeColor:'#FF6347'}); | |||
ll1 = brd. | |||
ll2 = brd. | |||
ll3 = brd. | |||
i5 = brd. | i5 = brd.create('intersection',[ll1,ll2,0],{name:"P",fillColor:'#9932CC',strokeColor:'#9932CC'}); | ||
brd.update(); | |||
</jsxgraph> | </jsxgraph> | ||
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<source lang="javascript"> | <source lang="javascript"> | ||
brd = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-1,4,12,-4], keepaspectratio:true}); | brd = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-1,4,12,-4], keepaspectratio:true}); | ||
p1 = brd. | p1 = brd.create('point', [0.5,-1.5] , {name:'A',fillColor:'red',strokeColor:'red'}); | ||
p2 = brd. | p2 = brd.create('point', [7.5,0.5] , {name:'B',fillColor:'red',strokeColor:'red'}); | ||
p3 = brd. | p3 = brd.create('point', [2,3] , {name:'C',fillColor:'red',strokeColor:'red'}); | ||
b1 = brd.create('segment',['A','B'],{name:''}); | |||
b2 = brd.create('segment',['A','C'],{name:''}); | |||
b3 = brd.create('segment',['C','B'],{name:''}); | |||
c1 = brd.create('circumcircle',['A','B','C'],{name:'', point: {visible: false}}); | |||
c1.setProperty('strokeColor:#AAAAAA'); | |||
l1 = brd.create('bisector',['B','A','C'],{name:'',visible:false}); // alpha | |||
l2 = brd.create('bisector',['C','B','A'],{name:'',visible:false}); // beta | |||
i1 = brd.create('intersection',[l1,l2,0],{name:'',visible:false}); | |||
pp1 = brd.create('perpendicularpoint',[i1,b1],{name:"C'",fillColor:'blue'}); | |||
pp2 = brd.create('perpendicularpoint',[i1,b2],{name:"B'",fillColor:'blue'}); | |||
pp3 = brd.create('perpendicularpoint',[i1,b3],{name:"A'",fillColor:'blue'}); | |||
c2 = brd.create('circumcircle',[pp1,pp2,pp3],{name:'', strokeColor: '#3CB371', point: {visible: false}}); | |||
c3[ | c3 = brd.create('circumcircle',[p3,pp2,pp3],{name:'', strokeColor: '#FF8C00', point: {visible: false}}); | ||
c4 = brd.create('circumcircle',[p2,pp1,pp3],{name:'', strokeColor: '#FF8C00', point: {visible: false}}); | |||
c5 = brd.create('circumcircle',[p1,pp2,pp1],{name:'', strokeColor: '#FF8C00', point: {visible: false}}); | |||
c4 = brd. | |||
c5 = brd. | |||
i2 = brd. | i2 = brd.create('otherintersection',[c3,c1,p3],{name:"C''",fillColor:'blue'}); | ||
i3 = brd. | i3 = brd.create('otherintersection',[c4,c1,p2],{name:"B''",fillColor:'blue'}); | ||
i4 = brd. | i4 = brd.create('otherintersection',[c5,c1,p1],{name:"A''",fillColor:'blue'}); | ||
ll1 = brd. | ll1 = brd.create('segment',[i2,pp1],{name:'',strokeColor:'#FF6347'}); | ||
ll2 = brd. | ll2 = brd.create('segment',[i3,pp2],{name:'',strokeColor:'#FF6347'}); | ||
ll3 = brd. | ll3 = brd.create('segment',[i4,pp3],{name:'',strokeColor:'#FF6347'}); | ||
i5 = brd. | i5 = brd.create('intersection',[ll1,ll2,0],{name:"P",fillColor:'#9932CC',strokeColor:'#9932CC'}); | ||
brd.update(); | |||
</source> | </source> | ||
[[Category:Examples]] | [[Category:Examples]] | ||
[[Category:Geometry]] | [[Category:Geometry]] |
Latest revision as of 09:56, 18 January 2021
Let ABC be a triangle and let the incircle intersect [math]\displaystyle{ BC }[/math], [math]\displaystyle{ CA }[/math], and [math]\displaystyle{ AB }[/math] at [math]\displaystyle{ A' }[/math], [math]\displaystyle{ B' }[/math], and [math]\displaystyle{ C' }[/math], respectively.
Let the circumcircles of [math]\displaystyle{ AB'C' }[/math], [math]\displaystyle{ A'BC' }[/math], and [math]\displaystyle{ A'B'C }[/math] intersect the circumcircle of [math]\displaystyle{ ABC }[/math] (apart from [math]\displaystyle{ A }[/math], [math]\displaystyle{ B }[/math], and [math]\displaystyle{ C }[/math]) at [math]\displaystyle{ A'' }[/math], [math]\displaystyle{ B'' }[/math], and [math]\displaystyle{ C'' }[/math], respectively.
Then [math]\displaystyle{ A'A'' }[/math], [math]\displaystyle{ B'B'' }[/math], and [math]\displaystyle{ C'C'' }[/math] meet in one point, [math]\displaystyle{ P }[/math].
The underlying JavaScript code
brd = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-1,4,12,-4], keepaspectratio:true});
p1 = brd.create('point', [0.5,-1.5] , {name:'A',fillColor:'red',strokeColor:'red'});
p2 = brd.create('point', [7.5,0.5] , {name:'B',fillColor:'red',strokeColor:'red'});
p3 = brd.create('point', [2,3] , {name:'C',fillColor:'red',strokeColor:'red'});
b1 = brd.create('segment',['A','B'],{name:''});
b2 = brd.create('segment',['A','C'],{name:''});
b3 = brd.create('segment',['C','B'],{name:''});
c1 = brd.create('circumcircle',['A','B','C'],{name:'', point: {visible: false}});
c1.setProperty('strokeColor:#AAAAAA');
l1 = brd.create('bisector',['B','A','C'],{name:'',visible:false}); // alpha
l2 = brd.create('bisector',['C','B','A'],{name:'',visible:false}); // beta
i1 = brd.create('intersection',[l1,l2,0],{name:'',visible:false});
pp1 = brd.create('perpendicularpoint',[i1,b1],{name:"C'",fillColor:'blue'});
pp2 = brd.create('perpendicularpoint',[i1,b2],{name:"B'",fillColor:'blue'});
pp3 = brd.create('perpendicularpoint',[i1,b3],{name:"A'",fillColor:'blue'});
c2 = brd.create('circumcircle',[pp1,pp2,pp3],{name:'', strokeColor: '#3CB371', point: {visible: false}});
c3 = brd.create('circumcircle',[p3,pp2,pp3],{name:'', strokeColor: '#FF8C00', point: {visible: false}});
c4 = brd.create('circumcircle',[p2,pp1,pp3],{name:'', strokeColor: '#FF8C00', point: {visible: false}});
c5 = brd.create('circumcircle',[p1,pp2,pp1],{name:'', strokeColor: '#FF8C00', point: {visible: false}});
i2 = brd.create('otherintersection',[c3,c1,p3],{name:"C''",fillColor:'blue'});
i3 = brd.create('otherintersection',[c4,c1,p2],{name:"B''",fillColor:'blue'});
i4 = brd.create('otherintersection',[c5,c1,p1],{name:"A''",fillColor:'blue'});
ll1 = brd.create('segment',[i2,pp1],{name:'',strokeColor:'#FF6347'});
ll2 = brd.create('segment',[i3,pp2],{name:'',strokeColor:'#FF6347'});
ll3 = brd.create('segment',[i4,pp3],{name:'',strokeColor:'#FF6347'});
i5 = brd.create('intersection',[ll1,ll2,0],{name:"P",fillColor:'#9932CC',strokeColor:'#9932CC'});
brd.update();