⨷Âì
¨§¾ÔÊÙ¨¹ìÇèÒ x = 30°
¾ÔÊÙ¨¹ì
(1) ∵ BC = CD <=> ∆BCD à»ç¹ ∆˹éÒ¨ÑèÇ ·ÕèÁÕ ∠C à»ç¹ÁØÁÂÍ´ <=> ∠CBD = ∠BDC
(2) ¡Ó˹´¨Ø´ P ·Õè·ÓãËé ☐ABDP à»ç¹ ☐ÁØÁ©Ò¡ => ...
• DP = AB
• AP = BD <=> AP = AC
• ∠BAP = 90°
• ∠BDP = 90° <=> ∠BDP = ∠ABD <=> ∠BDP + ∠BDC = ∠ABD + ∠CBD <=> ∠CDP = ∠ABC
(3) ÊѧࡵÇèÒ ∆CDP ≅ ∆ABC ´éǤÇÒÁÊÑÁ¾Ñ¹¸ìẺ ´-Á-´ (CD = BC, ∠CDP = ∠ABC, DP = AB) => CP = AC
∴ AC = AP = CP <=> ∆ACP à»ç¹ ∆´éÒ¹à·èÒ => ∠CAP = 60° <=> ∠BAC = x = 30° Q.E.D.