We know that the diagonals of a rhombus bisect (cut in halves) each other at 90 degrees.
Steps of construction:
Step 1. Draw a line segment BN = 6.5 cm. With radius greater than half of BN, draw arcs on both sides of BN with B and N as the center. The line joining these two intersections is the perpendicular bisector of BN. Let it intersect BN at O (Therefore, O is the midpoint of BN. It will also be the midpoint of DE!)
Step 2. With O as the center, draw two arcs on the perpendicular bisector with radius = (Since, O is the midpoint of DE.)
Step 3. The intersecting points are vertices D and E.
Step 4. Join D to B and N. Also join E to B and N.