jika

68/2 =34°

<aeb-<aec= 180-34
146°
Jadi <bec = 146°

<AEC = <BED (bertolak belakang)
<AEC + <BED = 68°
x + x = 68°
2x = 68°
x = 68° ÷ 2
= 34°
<AEC = 34°
<AEC + <BEC = 180° (berpelurus)
34° + <BEC = 180°
<BEC = 180° — 34°
<BEC = 146°
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