randomTriangleAngles.triangle()
What is the length of AD ? ( AD = DC )
init({ range: [ [-1, 12 ], [ -7, 2.5 ] ] }) var trA = new Triangle( [ 3, -4 ], [ 60, 60, 60 ] , 16 , {} ); var pointD = findIntersection( bisectAngle( trA.sides[ 0 ], reverseLine( trA.sides[ 2 ] ), 1 ), trA.sides[ 1 ] ); trA.draw() trA.labels = { "sides" : trA.niceSideLengths, "points": [ "A", "B", "C" ] }; trA.drawLabels(); var radius = lineLength( [ trA.circumCenter, trA.points[ 0 ] ] ); circle( trA.circumCenter, radius ); label( trA.circumCenter, "D", "right" ); line( trA.circumCenter, trA.points[ 0 ] ); line( trA.circumCenter, trA.points[ 2 ] );

Because side DAB and DAC are equal.

ThatAngles DAB and DAC are equal.