Verified Answer :

its about finding the equation of a circle from its general form equation:
x^2 + y^2 + 8x - 4y - 61 = 0
x^2 + 8x + 16 + y^2 - 4y + 4 = 61 + 16 + 4
(x + 4)^2 + (y - 2)^2 = 81
therefore the center is C(-4, 2), and the radius is 9

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