Des couches de cercles | Tangente

pencil of circles and radical axis in geometry | Tangente

Arbelos: Archimedes' figure of semicircles | Tangente

Circle of Apollonius: locus and fractal packing | Tangente

The last two sangaku solved | Tangente

Of all the sangaku on record, two have proved particularly difficult to solve. The Japanese mathematician Yamaguchi Kanzan (c. 1781–1850) collected them in his travel journal between 1817 and 1828.