Here is the problem.

Consider an isoceles triangle ABC.

Please see the diagram below and IGNORE the dots which are used to show the positions of the points. Point D is a point on side AB.

......................A

.................D

..............B__________C

suppose that side AB=side AC. angle BAC=20 degrees and angle BDC= 30 degrees.

Prove that side AD=side BC.

Please help. thanks