area of a cell
trapezoids and rhombusses
The area of the cell consists of 6 trapezoids and 3 rhombusses.
We write the area as a function of x = the length of the segment |BB1|.
The total area of the cell = 3 . (area rhombus) + 6 . (area trapezoid)
A(x)= 3 . + 6 .