∵ABCD是平行四边形,∴AD∥BC,∴∠DAB+∠ABC=180°,∵AP平分∠DAB,∴∠PAB=1/2∠DAB,∵AP⊥BP,∴∠PBA+∠PAB=90°,∴∠PBA+1/2∠DAB=90°,2∠PBA+∠DAB=180°,∴∠ABC=2∠PBA,∴BP平分∠ABC.⑵∵ABCD是平行四边形,∴...