First, draw a rough diagram

Step 1: The base CD measuring length 4 cm can be easily constructed.

Step 2: Draw a perpendicular to line DC at the point C. Let us call this line l.

Step 3: Draw an arc of radius 8 cm with point D as the center.

To locate the point B,
Step 4: Draw perpendiculars to DC and BC passing through D and B, respectively. The point where these lines intersect is the fourth point A.

It satisfies all conditions of the rectangle.