how do you make a concave hexagon with 4 triangles

Question

4 triangles put in to a rectangle cut out need to make a concave hexagon

Answer 1

 

The rectangle ABCD has been divided into 4 triangles: ABE (two sides marked in red dashes), EBF, EFD (two sides marked in blue dashes) and FBC.

Triangle ABE is shifted right to occupy triangle BB'E'; triangle EFD is shifted right to occupy triangle E'F'C.

The result is the green outlined concave hexagon EBB'E'F'F.