Reason: ≈ 1+∠4 = 180 (defined as a right angle), ∠ 1+∠ 2 = 180 (known).

∴∠2=∠4.

∴EF∥AB (internal dislocation angles are equal and two straight lines are parallel).

∴∠3=∠ADE (two straight lines are parallel with equal internal angles).

∫∠3 =∠B (known),

∴∠B=∠ADE (equivalent substitution).

∴DE∥BC (same angle, two straight lines are parallel).

∴∠ AED =∠∠ ACB (two straight lines are parallel and have the same angle).

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Can you keep asking if you don't understand?