Crockett's Triangles
Dave Richeson shared a great math story recently, about how the author of Harold and Purple Crayon was also a creative mathematician, and produced some intriguing mathart as well. One of his results was a construction of the regular heptagon. (Interesting because it's the first that canot be constructed by compass and straightedge alone.) It involves making an isosceles triangle that has base angles three times the measure of the other angle.
I made this sketch to investigate since I had never thought of it that way before, and was delighted by the results. (I probably shouldn't have been surprised, since the construction of the pentagon involves the 2x triangle, but... better late than never!)