Explanation
Standard equation of a circle with center (h,k) and radius r:
(x – h)^2 + (y – k)^2 = r^2
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(x – h)² → horizontal distance from center
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(y – k)² → vertical distance from center
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r² → radius squared
Example: Center (1, −2), radius = 3 → Equation: (x−1)^2 + (y+2)^2 = 9