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The center of the circle is at the origin, and the radius is 3 It's a process,
The standard equation of a circle: (x-a) ^ 2 + (y-b) ^ 2 = R ^ 2, a and B are the abscissa and ordinate of the center of the circle, R is the radius
So, there is no process, that is, x ^ 2 + y ^ 2 = 9
The equation of a circle with origin as its center and radius 4?
X^2+Y^2=4 ,
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