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x^2-2x+y^2-15=0   |Only one square to complete
(x-1)^2 -1 + y^2 -15 = 0
(x-1)^2 + y^2 = 16 
1) Circle with Center(1,0) and radius of 4
Standard Form of an Equation of a Circle is 
where Pt(h,k) is the center and r is the radius