设任一弦为AB,A(x1,y1),B(x2,y2),x1^2/4+y1^2/9=1,(1)x2^2/4+y2^2/9=1,(2)(1)-(2)式,(x1^2-x2^2)/4+(y1^2-y2^2)/9=0,9/4+[(y1-y2)/(x1-x2)]*{[(y1+y2)/2]/[(x1+x2)/2]}=0,其中,k=(y1-y2)/(x1-x2)=3/2,弦中点坐标M（ ...