∴∠A=∠D

∠∠ABP+∠APB+∠A = 180，∠APB+∠DPC+∠BPC= 180，∠BPC=∠A

∴∠ABP=∠DPC，

∴△ABP∽△DPC

∴ APCD = ABPD, namely AP2 = 25? Associated Press (AP)

Solution: AP= 1 or AP = 4.

(2)① It can be known from (1) that △ABP∽△DPQ.

∴ apdq = abpd, that is, x2+y = 25? x，

∴y=？ 12x2+52x？ 2( 1