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圆心 (2, -1) 半径 5 的圆方程。（答： (x-2)^2 + (y+1)^2 = 25 。）
圆心 (2, -1) 半径 5 的圆方程。（答： (x-2)^2 + (y+1)^2 = 25 。）
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