Answer: 1. Proof: Because? CPB= 138？ , so? APC=？ BPD= 180？ - 138? - 42? And because of what? A =42？ ,? B=69？ , so? A=？ APC？ D= 180？ -69? - 42? =69? =? B, so AC=CP, Pb = PD. And because CP= PD and AC= PB.

2. Solution:? AB=AC, AD equally divided? BAC，？ AD is also the high school line here in BC. BD= 1/2BC=5 cm，？ ADB=90？ . Again? B=45？ , bad =45? ,? AD=BD=5cm。

3. proof: in Rt△ACB, because? A=30？ ,? ACB=90？ , so? B=60？ ，BC = 1/2ab。 In Rt△BDC, because? B=60？ ,? BDC=90？ , so? BCD=30？ So BD= 1/2 BC, so BD= 1/2? 1/2AB= 1/4AB。

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