Construct a square of side 4 cm.

Step 1: Construct base = 4cm

Step 2: An angle of 90° is constructed at A and 4cm length is cut off

Step 3: Arcs of radius 4cm with centres at D and B are cut off and the point of intersection A is joined with D and B

ABCD is the required square with AB=BC=CD=DA=4cm