By definition of the area of a triangle, we have from
Fig 10 26,
Area of triangle ABC = 1 AB CD 2
⋅
But AB
|
b|
=
r  (as given), and CD = |
|
ar sinθ Thus,  Area of triangle ABC = 1 |
||
| sin
2 b
a
θ
r
r
 
1 |
|