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 trilinear coordinates 1:1:1.
The length angle triangle
where
The points trilinear coordinates incentral triangle .
See also Angle ,
Angle Bisector Theorem ,
Angle Trisection ,
Cyclic Quadrangle ,
Exterior Angle Bisector ,
Incenter ,
Incentral Triangle ,
Incircle ,
Isodynamic Points ,
Orthocentric System ,
Steiner-Lehmus Theorem Explore with Wolfram|Alpha References Altshiller-Court, N. College Geometry: A Second Course in Plane Geometry for Colleges and Normal Schools, 2nd ed., rev. enl. Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Dixon, R. Mathographics. Kimberling, C. "Triangle Centers and Central Triangles." Congr. Numer. 129 , 1-295, 1998. Mackay, J. S. "Properties Concerned with the Angular Bisectors of a Triangle." Proc. Edinburgh Math. Soc. 13 , 37-102, 1895. Pedoe, D. Circles: A Mathematical View, rev. ed. Referenced on Wolfram|Alpha Angle Bisector Cite this as: Weisstein, Eric W. "Angle Bisector." From MathWorld https://mathworld.wolfram.com/AngleBisector.html
Subject classifications 
, which has trilinear coordinates 1:1:1. 
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)],](http://mathworld.wolfram.com/images/equations/AngleBisector/NumberedEquation1.svg)
and 
. 
, 
, and 
have trilinear coordinates 
, 
, and 
, respectively, and form the vertices of the incentral triangle. 