Theory:
A general quadrilateral can be split into two triangles by drawing one of its diagonals.
Area of quadrilateral: The area is half the product of the diagonal and sum of heights of two triangles in it.
Area of quadrilateral = .
where \(d\) denotes the length of diagonal.
where and is denoted as heights.
Proof: Area of quadrilateral = .
Area of quadrilateral \(ABCD =\) (Area of \(△ ABC\)) \(+\) (Area of \(△ ACD\)).
\(=\) \(+\) .
\(=\) .
\(=\) .
Therefore, Area of quadrilateral \(=\) \(square units\).