Here is the equation of a circle: x2 + y2 - 6x - 20y + 105 = 0 Elena wants to find the center and radius of the circle. Here is what she's done so far.
Step 1: x2 - 6x + y2 – 20y = -105
Step 2: x2 - 6x + 9+ y2 - 20y + 100 = -105 + 9 + 100
Step 3: x2 - 6x + 9 + y2 - 20y + 100 = 4
1. What did Elena do in the first step?
2. Why did Elena add 9 and 100 to the left side of the equation in Step 2?
3. Why did Elena add 9 and 100 to the right side of the equation in Step 2?
4. What should Elena do next?