$$\left(x-p\right)^2+\left(y-q\right)^2=r^2$$  

$$\left(x+p\right)^2+\left(y+q\right)^2=r^2$$  

$$\left(x-p\right)^2-\left(y-q\right)^2=r^2$$  

$$\left(x+p\right)^2-\left(y+q\right)^2=r^2$$  

$$x^2-y^2=r^2$$  

$$x^2+y^2=r^2$$  

100

200

10

20

(1,-1)

(-1,1)

(1,1)

(-1,-1)

$$\left(x-4\right)^2+\left(y+2\right)^2=36$$  

$$\left(x+4\right)^2+\left(y-2\right)^2=36$$  

$$\left(x+2\right)^2+\left(y-1\right)^2=9$$  

$$\left(x-2\right)^2+\left(y+1\right)^2=9$$  

$$\left(x+2\right)^2+\left(y+3\right)^2=9$$  

$$\left(x+3\right)^2+\left(y+2\right)^2=9$$  

$$\left(x-2\right)^2+\left(y-3\right)^2=9$$  

$$\left(x-3\right)^2+\left(y-2\right)^2=9$$