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∵∠EFC=65° ∴∠FEA=∠EFC=65°(兩直線平行,內錯角相等) 又∵∠FEC=∠FEA(由折疊知) ∵∠FEA+∠FEC+∠BEC=180°(平角的定義) ∴∠BEC=180°-∠FEA-∠FEC=180°-2∠EFC=180°-130°=50°
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