Area of kites of rhombuses
A Rhombus is a foursided polygon having all four sides of equal length and whose opposite sides are parallel (every rhombus is a kite).
Each rhombus has two diagonals. The biggest one is called long diagonal and the smaller one is called short diagonal. (Note that the diagonals of a rhombus are perpendicular).
Area of kites and rhombuses

The area of any kite or rhombus is equal to onehalf the product of the lengths D and d of its diagonals.

What is the area when D=20 and d=2?