We know in rhombus diagonals bisect each other at right angle.
In ΔAOB
BO = \(\frac{BD}{2}\) = \(\frac{6}{2}\) = 3 cm
AO = \(\frac{AC}{2}\) = \(\frac{8}{2}\) = 4 cm
Using pythagorous theorem in ΔAOB
AB2 = AO2 + BO2
AB2 = 42 + 32
AB2 = 16 + 9
AB2 = 25
AB = \(\sqrt{25}\) = 5 cm
Therefore length of each side of a rhombus ABCD is 5 cm.