As
BP=BC⇒∠BPC=∠PCB
As exterior angle is equal to sum of two opposite interior angles
⇒∠BPC+∠PCB=4x
⇒∠BPC+∠BPC=4x
⇒2∠BPC=4x
⇒∠BPC=2x=∠PCB
Now DQ||CP
∠QDC=∠PCB [Corresponding angles]
⇒∠QDC=2x
As exterior angle is equal to sum of two opposite interior angles
⇒∠PCB=∠CPD+∠PDC
⇒2x=x+∠PDC
⇒∠PDC=x
As ∠QDC=2x and ∠PDC=x
⇒DP bisects ∠CDQ [Hence Proved]
As ∠PDC=x and ∠CPD and since sides opposite to equal angles are equal , hence
CP=CD [Hence proved]