{"type":"rich","version":"1.0","title":"geometric proof that sum_k=1..N { cos ( 2PI k/N + t ) } = 0","html":"<iframe src=\"https://www.desmos.com/calculator/vej1uznjnd?embed\" width=\"500px\" height=\"500px\" style=\"border: 1px solid #ccc\" frameborder=0></iframe>","width":500,"height":500}