1
圆心C(1,2),半径R=5
直线m:(2t+1)x+(t+1)y-7t-4=0 ,
(2x+y-7)t+x+y-4=0
假设2x+y-7=0,x+y-4=0,直线过定点p(3,1)
pc=√[(3-1)^2+(1-2)^2]=√5