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From module Geometry Basics
In the figure, ∠A\angle A∠A, ∠B\angle B∠B and ∠C\angle C∠C are right angles. If ∠AEB=40∘\angle AEB=40^{\circ}∠AEB=40∘ and ∠BED=∠BDE\angle BED=\angle BDE∠BED=∠BDE, then ∠CDE=\angle CDE=∠CDE= [See figure in original PDF]
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