Given information:
AD bisects
We are in a triangle that has been bisected , and therefore, the segment AD cuts the side BC of the triangle in two equal parts.
Also, since AD bisects the angle, <1 equals <2.
Step 1: Angle bisector defines two equal angles, then <1 = <2
They also tell us that angle <3 = <1 (premise)
Then, using transitive property we have:
<1 = <3
and <1 = <2 due to result of a bisection
then using transitive property:
<3 = <1 = <2
<3 = <2
Just lmake sure you use "transitive" property as the reason for the congruency in the last step.