What is the radius of a circle whose equation is x2+y2+8x−6y+21=0?

Complete the square for each variable: x² + 8x + y² − 6y + 21 = 0 becomes (x + 4)² + (y − 3)² = 4. A circle in this form has radius equal to the square root of the right-hand side, so its radius is √4 = 2 units. The correct choice is A, 2 units.

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