Rectangles and cubes

Rectangles and cubes are the building blocks of real analysis, whose objective is n dimensional real space, which we are not familiar with. We always study something new from the old which can be treated as the first step, just like we use the two or three dimensional space concepts areas and volumes as the preliminaries forward to higher dimension. Any basic geometry methods should be able to be used here, but may be not so useful or so clear. Then the more general description, measure, is developed.