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.

Area of rhombus: The area is half the product of the diagonals.

Area of rhombus $$=$$ $\frac{1}{2}\left({d}_{1}×{d}_{2}\right)$. (where, ${d}_{1}$ and ${d}_{2}$ denoted as diagonals of the rhombus)

Proof: Area of rhombus $$=$$ $\frac{1}{2}\left({d}_{1}×{d}_{2}\right)$.

Area of rhombus $$ABCD =$$ (Area  of  $$△ ACD$$) $$+$$ (Area  of  $$△ ABC$$)

$$=$$ $\left(\frac{1}{2}\phantom{\rule{0.147em}{0ex}}\mathit{AC}×\mathit{OD}\right)$ $$+$$ $\left(\frac{1}{2}\phantom{\rule{0.147em}{0ex}}\mathit{AC}×\mathit{OB}\right)$

$$=$$ $\frac{1}{2}\mathit{AC}\left(\mathit{OD}+\mathit{OB}\right)$

$$=$$ $\frac{1}{2}\mathit{AC}×\mathit{BD}$

$$=$$ $\frac{1}{2}\left({d}_{1}×{d}_{2}\right)$

Where ${d}_{1}$ and ${d}_{2}$ denoted as diagonals of the rhombus $$ABCD$$.

Therefore, Area of rhombus $$=$$ $\frac{1}{2}\left({d}_{1}×{d}_{2}\right)$ square units.