设弦的两端点坐标为(x1,y1),(x2,y2)则x1+x2=6,y1+y2=2,斜率k=(y1-y2)/(x1-x2)x1²－4y1²＝4x2²－4y2²＝4相减得：x1²－x2²＝4（y1²－y2²）（x1＋x2）（x1－x2）＝4（y1＋y2）...