延长CD至H,使DH=BP,连AH.
AB=AD ⇒RT△ABP≅RT△ADH
⇒AP=AH
BP+DQ=PQ
⇒DH+DQ=PQ
HQ=PQ
AQ=AQ
⇒△APQ≅△AHQ
∠PAQ=∠HAQ=∠BAP+∠DAQ=∠BAD/2=45°