Radius of a Scaled Circle Equation

First divide every term by 2 so the squared terms have coefficient 1: x² + y² − 4x + 6y − 3 = 0. Complete the square: (x − 2)² + (y + 3)² = 3 + 4 + 9 = 16. The radius is √16 = 4. Forgetting to divide by 2 first gives the wrong completing-the-square constants. TI-36X Pro tip: after dividing by 2, store the center (2 to x; (−)3 to y, using the (−) key, not minus) with sto→ and the x yzt abcd key, then evaluate x² + y² − 4x + 6y − 3. The result is −16, so r² = 16 and r = 4.