1. Circle Equation
Identify circle centers instantly.
"Find the center of \(x^2 + y^2 - 6x + 8y = 0\)."
- Step 1: Start with \(x^2 + y^2 - 6x + 8y = 0\).
- Step 2: Group x terms: \((x^2 - 6x) + (y^2 + 8y) = 0\).
- Step 3: Complete square for x: Half of -6 is -3, square is 9.
- Step 4: Add/subtract 9: \((x^2 - 6x + 9 - 9) + (y^2 + 8y) = 0\).
- Step 5: Complete square for y: Half of 8 is 4, square is 16.
- Step 6: Add/subtract 16: \((x^2 - 6x + 9) + (y^2 + 8y + 16 - 16) - 9 = 0\).
- Step 7: Move constants right: \((x^2 - 6x + 9) + (y^2 + 8y + 16) = 9 + 16\).
- Step 8: Factor squares: \((x - 3)^2 + (y + 4)^2 = 25\).
- Step 9: Identify center from \((x - h)^2 + (y - k)^2 = r^2\).
- Step 10: Center is (3, -4).
- Double the work, double the mistakes!
- Step 1: Half of -(-6) = 3.
- Step 2: Half of -(8) = -4.
- Center: (3, -4).