Question 1002386
Hi there,
x^2+y^2-8y=9
x^2 + y^2 - 8y - 9 = 0
Centre is obtained by halving the integers before
the x and y components and making them negative 
of the equation
Centre (0, 4)
...........
Radius = sqrt x coord of centre squared +
y coord of centre squared - the integer at 
the end of the equation (-9)
Radius = sqrt of 0^2 + 4^2 + 9
= sqrt25
= 5
Hope this helps :-)