ABCD is a a parallelogram. A circle passing through D , A,B cuts BC in P
Prove that DC = DP

DAB=90° and DPB=90°      Angle in the semicircle is 90°DAB+ DPB=180°  Therefore, ABPD is a cyclic quadrilateral.Now, suppose that DAB=θ DAB+DPB=180°   (ABPD is a cyclic quadrialteral)DPB=180°-θDAB=DCB=θ      (Opposite angles of a parallelogram are equal)DPC=180°-DPB  (Linnear pair)DPC=180°-180°+θDPC=θHence, DPC=DCP=θi.e., DC=DP  (Sides opposite to equal angle)

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