to #2:
1. Use two different values of k: k = r and k = s
2. You'll get two different circles:
2. Calculate the coordinates of the common points (points of intersection) by subtracting columnwise:
Divide by (r-s):
3. Plug in this term for x into the original equation:
Solve for y:
4. Calculate the x-coordinate. You'll get 2 points whose coordinates are not depending on k, that means each circle passes through these two points: