There are two vectors (d and c). d dot c will equal 50. The angle between them is 60 degrees (when the two vectors are tail to tail). What is ID X CI ?
In order to do this equation, you need to know that d dot c= |d||c|cos(theta) where theta is the angle between them. I started to write "to find ID X CI" you would have to know what 'ID' and 'CI' mean" when it hit me that you mean |D X C|, the length of DXC. Of course, to do that you have to know that that length is given by |D||C| sin(theta).
I have a rather roundabout solution . . .
We have parallelogramCode:C * - - - - - * B / \ / / \ / c / \ / / \ / / 60d \ / A * - - - - - * D d
. . where
We know that is the area of the parallelogram.
So we have: .
The area of is given by: .
The area of parallelogram is: .