In the isosceles triangle ABC, the angle a is equal to 20 degrees, AB is equal to AC, D is on AC, and ad is equal to BC. Find the size of the angle abd
AB = AB, angle a = 20 degrees, then angle B = 80 degrees. Take AB as the side length, make equilateral triangle Abe (point E and C are on both sides of AB), connect de. then AE = AB = AC; and ∠ DAE = ∠ DAB + ∠ BAE = 80 ° = ∠ C. and ad = BC. So ⊿ DAE ≌ Δ BCA (SAS), get de = AB; and ∠ AED = ∠ cab = 20 °. De = AC = AE = be, then points a, D, B are on the basis of point E
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