Step-by-step explanation:
Okay, so the triangle would look something like this:
see the image attached
Since AB=AC, which is given; <ABD = <ACD, because they are the angles opposite from the congruent sides of the isosceles triangle; and <ADB=<ADC, as AD is the bisector*; ΔABD ≅ ΔACD using SAA/AAS (side-angle-angle) congruencey.
*If the bisector of an angle in a triangle meets the opposite side at its midpoint, then the triangle is isosceles, and vice versa
(I haven't done Geometry in a while so I hope that's correct :) )
