Because the segment BC is 1cm, and ABCD is constructed of 4 identical rectangles (In the figure) => The width of 4 small rectangles is: \(1:2=\dfrac{1}{2}\)(cm)

The area of 1 small rectangle is: \(1.\dfrac{1}{2}=\dfrac{1}{2}\left(cm^2\right)\)

Then the area of 4 small rectangle is: \(\dfrac{1}{2}.4=2\left(cm^2\right)\)

Then the segment AB is: \(2:1=2\left(cm\right)\)