angle1=angle2
angle3=angle4
1+3=2+4
angleBAC=angleDAC
In triangle BAC and triangle DAC
AB=AD(given)
angleBAC=angleDAC(proved)
AC=AC(commom side)
triangleBAC is congruent to triangleDAC by SAS congruence rule
angleACP=angleACQ(CPCT)
In triangleACP and triangleACQ
angle3=angle4(given)
angleACP=angleACQ(proved)
AC=AC(common side)
triangleACP is congruent to triangleACQ by ASA congruence rule
AP=AQ(CPCT)