習題6D    NO:1,6,14

1.        參看附圖
               y=95°
           y+x=180°(直線上的鄰角)
               x=180°-95°
               x=85°

6.        參看附圖
           36°+60°=x(△外角)
                      x=96°
           ∴∠ADE=96°
                      x=a(圓內接四邊形外角)
                      a=96°
        36°+60°+y=180°(△內角和)
                      y=180°-36°-60°
                      y=24°
            ∴∠DEF=24°

14.    參看附圖
                a=90°(半圓上的圓周角)
                b=65°(圓內接四邊形外角)
         a+b+c=180°(△內角和)
   90°+65°+c=180°
                 c=180°-90°-65°
                 c=25°
             x+c=65°(內錯角,AB//DC)
             x+25°=65°
                   x=65°-25°
              ∴∠x=40°
         ∴∠DBC=40°

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