maths
posted by Shane .
A circle x^2 + y^ + 2x  2y 1 = 0 expressed in the following form (xh)^2 + (yk)^2 = r^2 where h, k are the coordinates of the centre. How is r the radius given?

eh? r is the radius. r = √r^2
Not sure what you mean by "how is r given?" Its square is part of the equation, as are h and k.
For this particular circle, we have
x^2+2x + y^22y = 1
x^2+2x+1 + y^22y+1 = 1+1+1
(x+1)^2 + (y1)^2 = 3
so, r = √3