x2+y2-8x-4y+11=0
(x-4)^2+(y-2)^2=3^2
圆心A(4,2),半径R1=3
x2+y2+4x+2y+1=0
(x+2)^2+(y+1)^2+2^2
圆心B(-2,-1),半径R2=2
|PQ|的最小值=AB-R1-R2=((4+2)^2+(2+1)^2)^(1/2)-(3+2)=3(根号5)-5
|PQ|的最大值=AB+R1+R2=3(根号5)+5
2.
x2+y2-4x-14y+45=0
(x-2)^2+(y-7)^2=8
圆心A(2,7),半径=2*(根号2)
x2+y2+4x-6y+13
=(x+2)^2+(y-3)^2
就是P(x,y)到B(-2,3)得距离的平方
AB^2=(2+2)^2+(7-3)^2=32
AB=4*(根号2)
x2+y2+4x-6y+13最小值=(4*(根号2)-2*(根号2))^2=8
x2+y2+4x-6y+13最大值=(4*(根号2)+2*(根号2))^2=72