Hi,



Standard Form of an Equation of a Circle is  

where Pt(h,k) is the center and r is the radius

x^2+y^2+4x-4y-1=o      |Completing square

(x+2)^2 - 4 + (y-2)^2 - 4 - 1 = 0

(x+2)^2  + (y-2)^2 = 9 

  r = 3 

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