Prove that a triangle that has two congruent angles is isosceles I'm having some trouble with the following problem:

Prove that a triangle that has two congruent angles is isosceles

I tried to prove this by separating it into two triangles and use the ASA or the SAS postulate. However, I am stuck. I need some help. Thank you!

If you bisect the vertex angle, you find that you have created two congruent triangles. The triangles are congruent because of AAS congruence.  Because of CPCTC, the sides are congruent as well. It is hard to describe. See this image: 

