假设b(x,y)
则x^2+y^2=25(1)即
6x-8y=50(2)
a-b=(6-x,-8-y)
(1)-(2)得
x^2-6x+y^2+8y+25=0
=>
(x-3)^2+(y+4)^2=0
=>
x=3,y=-4
=>
a-b=(3,-4)
没错了
不小心把-8-y算成了-8-4应该是-8+4