✔ 最佳答案
9(a)
2 x∠BPA = ∠BOA (圓心角兩倍於圓周角)
∠BPA = 40° / 2
∠BPA = 20°
9(b)
連合OP
2 x∠BCP = ∠BOP (圓心角兩倍於圓周角)
∠BOP = 50° x 2
∠BOP = 100°
OB = OP
ΔBOP 是一個等腰三角形
∠OBP = ∠OPB
∠OBP + ∠OPB + ∠BOP = 180°
∠OBP = (180° - 100°) / 2
∠OBP = 40°
OA = OB
ΔAOB 是一個等腰三角形
∠OAB = ∠OBA
∠OAB + ∠OBA + ∠AOB = 180°
∠OBA = (180° - 40°) / 2
∠OBA = 70°
∠ABP = ∠OBA - ∠OBP
∠ABP = 30°
17.
∠ABD = 90° (半圓上的圓周角是一個直角)
∠BAD = 65° (圓內接四邊形的外角)
∠ADB + ∠ABD + ∠BAD = 180°
∠ADB = 25°
∠ADC = 65° (平行線上的錯角)
∠BDC + ∠ADB = ∠ADC
∠BDC = 40°
14.
將AP伸延至細圓的邊,交點設為Q
連接CQ成一條直線
ABCQ為細圓內接的四邊形
∠AQC + ∠ABC = 180° (圓內接四邊形對角互補)
∠AQC = 180° - 110°
∠AQC = 70°
∠AQC = ∠AOC / 2 (圓心角兩倍於圓周角)
∠AOC = 140°
AOCP為大圓內接的四邊形
∠AOC + ∠APB = 180° (圓內接四邊形對角互補)
∠APB = 40°