What is the radius of a circle whose equation is x squared plus y squared minus 10 x plus 6 y plus 18 is equal to 0 ?

Complete the square for each variable: x² − 10x + y² + 6y + 18 = 0 becomes (x − 5)² + (y + 3)² = 16. A circle in this form has radius equal to the square root of the number on the right, so the radius is √16 = 4 units. The correct choice is B, 4 units.

AI-written and checked against the verified answer.