This construction to trisect a line segment comes from Proofs Without Words by Scott Coble, via this page. The code looks like this:
scene .point(width/7*3, height/3) .point(width/7*5, height/3) .segment(0,1) .circle(0,1) .circle(1,0) .line(0,2) .segment(0,3) .segment(4,1) .segment(2,6)
Also check out this one.