You need to draw a line which bisects an angle.
There are 4 ways to approach this goal.
Approach 1: use Construction Line command to bisect. Run command XLINE, then follow below steps:
Infinite line: Bisect/Horizontal/Vertical/Angle/Offset/<Point along Line>: b (input B)
Entity/<Vertex point>: (select the vertex of the angle)
Bisection angle start point: (select one edge of the angle)
Bisection angle end point: (select another edge of the angle)
Press Enter, now you can get the bisector.
Approach 2: use angular dimension
Draw an angular dimension for the angle, then run Line command to draw the bisector. First select the vertex of the angle as the first point of the line, then snap to the midpoint of the angular dimension arc. Now the bisector is available and the angular dimension could be deleted.
Approach 3: use Arc command.
Firstly draw an accessorial arc using the angular vertex as center with start from one sides of the angle to the other side. Then draw a line with the angular vertex as starting point, and the midpoint of the arc as end point. Now the bisector comes out. This is similar to Approach 2
Approach 4: use below LISP program to draw a bisector.
Run APPLOAD to load the program and then run DIVDANG to execute it.