We use this theorem:

If the diagonals of a quadrilateral bisect each other, the 
quadrilateral is a parallelogram.

1. Draw a line 5.2 cm long. 

2. Open the compass to 1/2 the length
of the shorter diagonal (1/2 of 6cm is 3cm)

3. Placing the sharp point of the compass on the right end of the
line, and swing an arc (the one I have in green).

4. Open the compass to 1/2 the length
of the longer diagonal (1/2 of 6.4cm is 3.2cm)

5. Placing the sharp point of the compass on the left end of the
line, and swing an arc (the one I have in red).



6. Draw a line 6cm long from the right end of the line through
the point where the arcs cross.

6. Draw a line 6.4cm long from the left end of the line through
the point where the arcs cross.



7. Draw in the other three sides of the parallelogram.



Edwin