设过P点弦为AB,A（x1,y1),B(x2,y2),x1^2/9+y1^2=1,(1)x2^2/9+y2^2=1,(2)(1)-（2）式,(x1^2-x2^2)/9+(y1^2-y2^2)/4=0,4/9+[(y1-y2)/(x1-x2)]*{[(y1+y2)/2/[(x1+x2)/2]}=0,(3)弦直线方程斜率k=(y1-y2)/(x1-x2),(y1+y2)...