抛物线C:y^2=4x①的焦点为F(1,0),
设过点K(-1,0)的直线L：x=my-1,
代入①,整理得
y^2-4my+4=0,
设L与C 的交点A(x1,y1),B(x2,y2),则
y1+y2=4m,y1y2=4,
点A关于X轴的对称点D为(x1,-y1).
1.BD的斜率k1=（y2+y1)/(x2-x1)=4m/[m(y2-y1)]=4/(y2-y1),
BF的斜率k2=y2/(x2-1).
k1=k24(x2-1)=y2(y2-y1),4x2=y2^2,
上式成立,∴k1=k2,∴点F在直线BD上.
2.向量FA*FB=(x1-1,y1)*(x2-1,y2)=(x1-1)(x2-1)+y1y2=(my1-2)(my2-2)+y1y2
=(m^2+1)y1y2-2m(y1+y2)+4=4(m^2+1)-8m^2+4=8-4m^2=8/9,
∴m^2=16/9,m=土4/3.
取y2-y1=√(16m^2-16)=4√（m^2-1)=(4/3)√7,
∴k1=3/√7,BD:y=(3/√7）（x-1).
易知圆心M在x轴上,设为(a,0),M到x=(4/3)y-1和到BD的距离相等,即
|a+1|/(5/3)=|（3/√7）（a-1)|/(4/√7）,
∴4|a+1|=5|a-1|,-1