AC and BD are diagonals of the rhombus ABCD with side = 10 cm One diagonal of a rhombus is half the other, let AC = 4x cm ⇒ BD = 2x cm Diagonal of a rhombus perpendicularly bisect each other. ⇒ OD = x cm and OC = 2x cm In ∆OCD, ⇒ (OC)2+(OD)2=(CD)2 ⇒ (2x)2+(x)2=(10)2 ⇒ 4x2+x2=100 ⇒ x2=