j
i
k
k
j
i
i
k
j
× = −
×
= −
×
= −
8 If 
aand
rb
r
represent the adjacent sides of a triangle then its area is given as
1 |
|
2 a
b
 
r
r By definition of the area of a triangle, we have from
Fig 10 26,
Area of triangle ABC = 1 AB CD