group x and y's
and comlete the sqare for each
x²+y²-2y-15=0
group
(x²)+(y²-2y)-15=0
take 1/2 of linear coefient and squaer it and add negative and positive iniside
-2/2=-1, (-1)²=1
(x²)+(y-2y+1-1)-15=0
factor prefect squares
x²+(y-1)²-1-15=0
x²+(y-1)²-16=0
add 16 to both sides
x²+(y-1)²=16
which can be rewritten in form
(x-0)²+(y-1)²=4²
center is at (0,1) and has a radius of 4
