Question 1131761
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The vertex angle BAC is 120 degrees; the angle bisector creates two angles of 60 degrees each.<br>
Since the triangle is isosceles, the angle bisector AH is perpendicular to side BC.<br>
Then triangle ADH is a 30-60-90 right triangle.<br>
Given AD = a and HD = b, with ADH a 30-60-90 right triangle, we know AH = 2a.  So the perimeter of triangle ADH is 2a+a+b = 3a+b.