In the figure below, △ABC ≅ △BED, ∠DEB = 115∘ and ∠CAB = 25∘, find ∠BDE.
40°
Since △ABC ≅ △BED
∠DEB = ∠CBA = 115∘
∠CAB = ∠DBE = 25∘
∠CBA,∠DBE and ∠CBD from a linear pair.
∠CBA + ∠DBE + ∠CBD = 180∘
So, ∠CBD = 40∘
∠CBE + ∠BED =180∘
So, BC ∥ ED
∠BDE = ∠CBD = 40∘ (Alternate interior angles)