Download 9-5 Notes

9-5 Trigonometry and Area
Essential Question: Is it possible to find the
area of a triangle without knowing its height?
**Remember the formula ½ ap ?
The formula was easy to use if the apothem and
radius formed 30-60-90 or 45-45-90 triangles, but
what kind of triangles do octagons form? decagons?
pentagons?
Using trig., we can use the same formula on any
regular polygon.
Ex. Find the area of a regular pentagon with 8 cm.
sides.
Theorem 9-1
Area of a
Triangle
Given SAS
The area of a
B
triangle is one half
a
c
the product of the
lengths of two
A
b
C
sides and the sine
of the included
Area of triangle
angle.
ABC =
1
bc(sin a )
2
Ex. Find the area of the triangle.
34 km
28
39 km