In a triangle ABCABCABC, AB=ACAB=ACAB=AC. If ∠A=40∘\angle A = 40^\circ∠A=40∘, find ∠B\angle B∠B.
70∘70^\circ70∘
40∘40^\circ40∘
50∘50^\circ50∘
80∘80^\circ80∘