是不是應該請二位為三隻虎大哥解說一下，我的解法大家似乎看不懂?
有勞二位了。
~~~~~~~~~這是分隔線~~~~~~~~~~~
其實大意是這樣
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AX = AB + BC − CA
----------------------
2
AY = BC + CA − AB
----------------------
2
AD = AE = CA + AB − BC
-----------------------------
2
BD = AB − AD = AB − CA + AB − BC
------------------------------------------
2
= AB + BC − CA
------------------
2
= AX.
~~~~~~~~~這是分隔線~~~~~~~~~~~
腦袋快炸掉了這種題目
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∠BIC = 180◦− ∠IBC − ∠ICB = 180◦− 0.5∠ABC − 0.5∠ACB
= 180◦− 0.5(∠ABC + ∠ACB) = 180◦− 0.5(180◦− ∠BAC) = 90◦
+ 0.5∠BAC
∠BAC < 60◦
2∠BAC < 90◦+0.5∠BAC,
=∠BOC < ∠BIC
∠BPC < ∠BOC = 2∠BAC < 120◦
∠BPC = 180◦− (∠PBC + ∠PCB) < 180◦−(∠B + ∠C)/2
= 90 + ∠A/2< 120◦