Sangaku what does it mean?

Sangaku are geometric drawings from Japan that raise fascinating geometric problems.

Translated literally as "mathematical table" sangaku are wood clipboards with figures in vivid colors that, during the Edo period (1603 to 1868), used to be placed in Shinto temples and sanctuaries as votive offerings to the spirits of nature.

They could be found hanging in public places as challenges to visitors, challenging them to participate collaboratively in the solution of the problem.

These tablets were made by people from diverse backgrounds, from samurais to traders, farmers and even children, not only for what we would today call a professional mathematician.

Full of triangles, circles, ellipses and spheres that appeared one into the other to pose challenges wiht equal artistic and mathematical value. Currently, more than 800 sangaku that were spread among almost all prefectures in Japan, have been recovered and classified.

Most of them can be solved using Euclidean geometry, although many others require modern mathematics such as calculus or affine transformations.

Eventhough the sangaku had merely recreational purposes, they include some important theorems of Western mathematics.