令y=k(x-2)+1=kx-2k+1,代入椭圆方程：9x^2+25[k^2x^2+(2k-1)^2-2kx(2k-1)]=225(9+k^2)x^2-50k(2k-1)x+25(2k-1)^2-225=0设M(x,y),由中点定义及韦达定理得：x=(x1+x2)/2=25k(2k-1)/(9+k^2)将k=(y-1)/(x-2)代入得：x[9+...