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From module Geometry Basics
If ∠A=60∘\angle A=60^{\circ}∠A=60∘, ∠E=40∘\angle E=40^{\circ}∠E=40∘ and ∠C=30∘\angle C=30^{\circ}∠C=30∘, then ∠BDC=\angle BDC=∠BDC= [See figure in original PDF]
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