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: