y1²=4x1①；y2²=4x2②,①-②得：y1+y2=4/k ③①+②得4(x1+x2)=y1²+y2²=(y1+y2)²-2y1y2又y1y2=-p²,联立③得x1+x2=4/k²+2,由于(x1+x2)/2=√(r²-4),从而(2/k²+1)²=r...