Theory:

A special quadrilateral is also like a general quadrilateral method of splitting into two triangles to find a formula for the area of rhombus. In a rhombus, diagonals are perpendicular bisector of each other.
rhombus main.PNG
 
Area of rhombus: The area is half the product of the diagonals.
rhombus.PNG
 
Area of rhombus \(=\) 12d1×d2. (where, d1 and d2 denoted as diagonals of the rhombus)
 
Proof: Area of rhombus \(=\) 12d1×d2.
 
Area of rhombus \(ABCD =\) (Area  of  \(△ ACD\)) \(+\) (Area  of  \(△ ABC\)).
 
 
\(=\) 12AC×OD \(+\) 12AC×OB
 
\(=\) 12ACOD+OB
 
\(=\) 12AC×BD
 
\(=\) 12d1×d2
 
Where d1 and d2 denoted as diagonals of the rhombus \(ABCD\).
 
Therefore, Area of rhombus \(=\) 12d1×d2 square units.