Angle Bisector
The (interior) bisector of an angle, also called the internal angle bisector (Kimberling 1998, pp. 11-12), is the line or line segment that divides the angle into two equal parts.
The angle bisectors meet at the incenter 
, which has trilinear
coordinates 1:1:1.
The length 
of the bisector 
of angle 
in the above triangle 
is given by
![t_1^2=a_2a_3[1-(a_1^2)/((a_2+a_3)^2)],](/National_Library/20161222123739im_/https://mathworld.wolfram.com/images/equations/AngleBisector/NumberedEquation1.gif) |
where 
and 
.
The points 
, 
, and 
have trilinear
coordinates 
, 
, and 
, respectively, and form the vertices of the
incentral triangle.
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