國二數學問題急急急?拜託!!?

BD = CD,
∴ ∠B = ∠DCB
CD = CE
∴ ∠E = ∠CDE

∠A = 66°, ∠B = 40°
∴ ∠BCA = 74°
∴ ∠DCA = ∠BCA - ∠DCB
         = 74°-40° = 34°
   ∠ADC = 180° - 34° - 66° = 80°

   ∠A + ∠ADE + ∠E = 180°
      = ∠A + ∠ADC + ∠CDE + ∠E
      = 66° + 80° + 2∠E
∴ ∠CDE = ∠E
      = (180°-66°-80°)/2 = 17°

△DCF 中, ∠CDF = 17° < ∠DCF = 40°
大角對大邊, ∴ DF > CF