2. The Area of a Triangle A C B
How do we calculate the area of triangle ABC?
The base and height in the above formula must be at right angles (or perpendicular).
But we will not always know a perpendicular height.
In this case there is a second formula we can use:
Area = ½absinC

3. Example 1 Find the area of this field in hectares. Area = ½absinC 413m
68
= ½  413  234  sin68
= 44802·45m2
= 4·48ha
Remember
1 hectare =
100m
10 000m2
10 000m2

4. Example 2 P Q R
Find the area of PQR, if P = 56°, q = 23·6m and r = 43·6m.
23·6m
43·6m
56
Draw a diagram first.
Label diagram.
Area = ½qrsinP
= ½  23·6  43·6  sin56
= 426·52m2

5. Today’s work
Exercise 6C
Pg 180
#1ad, 2, 3