The classical chineese tangram is nearly 2500 years old, the name is may be based on the Tang dynasty
In Europe this game become popular during
the 18th century and is also today of some interest.
At least if you are counting the hits within a Google search with app. 7.6 million hits.
The traditional chineese tangram consist of
two big triangles
one medium sized triangle
and two small triangles
and a rhombus
With A = 1 and B = 2 C and D will be as follow C = √ 8 ~ 2,828 and D = √ 2 ~ 1,414