Fill in the blanks to make the correct statement.
If the diagonal d of the quadrilateral is doubled and the heights h1 and h2 is falling on d are halved, then the area of quadrilateral is _________.
Let ABCD be a quadrilateral ,where h1 and h2 are height on the diagonal BD = d
Then , area of quadrilateral ABCD = (h1 + h2)BD
= × 2d
= (h1 + h2) × d