设点D(x,y) (y-1)/(x-1)=(-2-4)/(4+4)=-3/4 y=-3x/4+7/4 (x-1)²+(-3x/4+7/4-1)²=25 (x-1)²=16 x-1=±4 x=5 y=-2 或x=-3 y=4 所以点D为(5,-2)或(-3,4)
