设A(x1，y1)，B(x2，y2)则x1²/9+y1²/4=1x2²/9+y2²/4=1相减得到，(x1+x2)(x1-x2)/9+(y1+y2)(y1-y2)/4=0∵P是中点，∴x1+x2=2，y1+y2=2∴ 2(x1-x2)/9+(y1-y2)/2=0∴k=(y1-y2)/(x1-x2)=-9/4∴直线方程为y-1=-9/4·(x-1)即4x+9y-13=0
