y-1=k(x-2)y=kx+(1-2k)代入(4-9k²)x²-18k(1-2k)x-9(1-2k)²-36=0x1+x2=18k(1-2k)/(4-9k²)则重点横坐标=(x1+x2)/2=9k(1-2k)/(4-9k²)=29k-18k²=8-18k²k=8/9所以是8x-9y-7=0...