∴∠∠∠1=∠ ANC Two straight lines are parallel, and the included angles are equal.

∵AB//CD is known.

∴∠

∴∠C=∠ 1 equivalent substitution

∫∣≈ 1 = 60 is known.

C = 60 equivalent substitution

2. Proof: ∠BAD=∠CAD

Ef⊥bc ∵ad⊥bc (known)

∴∠ EFD = _ _ ∠ ADC _ _ _ _ = 90 (vertical definition)

∴EF//AD (same angle, two parallel straight lines)

∴∠ E = _ _ ∠ CAD _ _ _ _ two straight lines are parallel and have the same angle)

∫≈ 1 =∠E (known)

∵EF//AD is known.

∴∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠873

∴∠BAD=∠CAD (equivalent substitution)

Let's ask two questions first.