What is the radius of a circle whose equation is x2+y2−10x+6y+18=0?

Complete the square for each variable: (x − 5)² − 25 + (y + 3)² − 9 + 18 = 0. Rearranging gives (x − 5)² + (y + 3)² = 16. In the standard circle equation, the right side is the radius squared, so the radius is √16 = 4 units, choice B.

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