Answers

仮定より∠BAD=∠CAD
AD平行ECより錯覚は等しいので
∠DAC=∠ECA
同位角は等しいので
∠BAD=∠AEC
よって∠ACE=∠AEC
2組の角が等しいので
△ACEは二等辺三角形となる

統一感なくてすみません…

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