Move the circles around! Say you take the two tangent lines of two circles, and you draw a point where they intersect. Now do this with each pair of three circles. The points will always be in one line, as you can see this the blue line. It doesn't matter what size the circles are. Moving the red circle is smooth, but the other ones you have to let go before you see what happens.
I saw this on a 3blue1brown video, and I decided to code it! Here is his channel: https://www.youtube.com/c/3blue1brown
