The mathematics being highlighted how the coordinates are always changing for the points. To create this I chose a circle with a center and radius and put the radius as 5. I placed it down and then continued. I then chose semicircle with 2 points through it and placed 8 semicircles along the whole circle. You then click each point of each semicircle and click animate You then press pause and click on line H then choosing object properties. You go to advanced settings; for red you put x(H), for green y(H), for blue 5x(H), and can then be done with that. Next you click on point h and then f. You then click line h and click trace on, You are then done, can hit play, and watch it fill with color.