**Example 6:** Determine the resultant
moment of the two forces about line aa.

(Move the mouse pointer over the figure to see the moment
vector)

**Solution:** We begin by calculating the
moment of force about
line aa as

where

Using the triple scalar product, we find

Repeating the calculations for , yields

where

Therefore, the resultant moment about line aa is

We can express the moment resultant in Cartesian vector form as