what you do is get into the form
(x-h)^2+(y-k)^2=r^2
(h,k) is center
r=radis
complete the square with x and y
x^2+y^2-2x+4y-11=0
group x and y terms together
(x^2-2x)+(y^2+4y)-11=0
take 1/2 of linear coefieicnt and add postive and negative
for x^2-2x, -2/2=-1, (-1)^2=1
for y^2+4y, 4/2=2, 2^2=4
(x^2-2x+1-1)+(y^2+4y+4-4)-11=0
complete the square
(x-1)^2-1+(y+2)^2-4-11=0
add like terms
(x-1)^2+(y+2)^2-16=0
add 16 both side
(x-1)^2+(y+2)^2=16
(x-(1))^2+(y-(-2))^2=4^2
(x-h)^2+(y-k)^2=r^2
(h,k)
(1,-2)
r=4
center is (1,-2)
radius is 4 units
