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⨷Âì
¨§¾ÔÊÙ¨¹ìÇèÒ x = 6°
¾ÔÊÙ¨¹ì 1
(1) ∵ ∠BAC = ∠ABC ⇔ ∆ABC à»ç¹ ∆˹éÒ¨ÑèÇ ·ÕèÁÕ ∠C à»ç¹ÁØÁÂÍ´ ⇔ BC = AC ⇔ BC = BP
(2) µèÍ AC ÍÍ¡ä»Âѧ¨Ø´ Q â´Â·Õè AQ = AB
¨ÐàËç¹ÇèÒ ∆APQ ≅ ∆ABP ´éǤÇÒÁÊÑÁ¾Ñ¹¸ìẺ ´-Á-´ (AP = AP, ∠PAQ = ∠BAP, AQ = AB) ⇒ PQ = BP
¹Í¡¨Ò¡¹Ñé¹ Âѧä´éÇèÒ ∠AQP = ∠ABP ⇔ ∠AQP = 2x
(3) ¾Ô¨ÒÃ³Ò ☐ABPQ ¨Ðä´éÇèÒ ∠BPQ (ÁØÁãËè) = 360° - 10x ⇔ ∠BPQ (ÁØÁàÅç¡) = 10x
ÊѧࡵÇèÒ BC = BP áÅÐ ∠CBP = 2(∠CQP) ⇒ ¨Ø´ B à»ç¹¨Ø´ÈÙ¹Âì¡ÅÒ§¢Í§Ç§¡ÅÁ·ÕèÁÕ ∆CPQ Ṻ㹠⇒ BP = BQ
∴ BP = BQ = PQ ⇔ ∆BPQ à»ç¹ ∆´éÒ¹à·èÒ ⇒ ∠BPQ = 60° ⇔ 10x = 60° ⇔ x = 6° Q.E.D.
¾ÔÊÙ¨¹ì 2 (â´Â¤Ø³ Angel Lazo HK)
(1) ∵ ∠BAC = ∠ABC ⇔ ∆ABC à»ç¹ ∆˹éÒ¨ÑèÇ ·ÕèÁÕ ∠C à»ç¹ÁØÁÂÍ´ ⇔ BC = AC ⇔ BC = BP ⇔ ∆BCP à»ç¹ ∆˹éÒ¨ÑèÇ ·ÕèÁÕ ∠B (= 4x) à»ç¹ÁØÁÂÍ´ ⇔ ∠BCP (= ∠BPC) = 90° - 2x
(2) ¡Ó˹´¨Ø´ Q º¹ AB ·Õè·ÓãËé PQ ⊥ AB áÅСÓ˹´¨Ø´ R º¹ AC ·Õè·ÓãËé PR ⊥ AC
¨ÐàËç¹ÇèÒ ∆APR ≅ ∆APQ ´éǤÇÒÁÊÑÁ¾Ñ¹¸ìẺ Á-Á-´ (∠ARP = ∠AQP, ∠PAR = ∠PAQ, AP = AP) ⇒ PR = PQ
(3) ¡Ó˹´¨Ø´ S º¹ CP ·Õè·ÓãËé BS ⊥ CP ⇒ BS à»ç¹ÊèǹÊÙ§¢Í§ ∆BCP ⇒ CS = PS áÅÐ ∠PBS (= ∠CBS) = (∠CBP)/2 = 2x
¨ÐàËç¹ÇèÒ ∆BPS ≅ ∆BPQ ´éǤÇÒÁÊÑÁ¾Ñ¹¸ìẺ Á-Á-´ (∠BSP = ∠BQP, ∠PBS = ∠PBQ, BP = BP) ⇒ PS = PQ ⇔ CS = PQ
(4) ÊѧࡵÇèÒ ∆CPR à»ç¹ ∆ÁØÁ©Ò¡ ·ÕèÁÕ ∠R à»ç¹ÁØÁ©Ò¡ áÅÐ CP = 2‧PR ⇒ ∠PCR = 30°
¾Ô¨ÒÃ³Ò ∆ABC ¨Ðä´éÇèÒ ∠BAC + ∠ABC + ∠ACB = 180° ⇔ 6x + 6x + (120° - 2x) = 180° ⇔ x = 6° Q.E.D.