6.5 The Cosine Ratio
B
Hypotenuse
Opposite
C
Adjacent
A
The cosine ratio for acute angle A, is the ratio of the length of the
adjacent side (to angle A) over the length of the hypotenuse.
adjacent
__________
cos A = hypotenuse
1
Example 1
Use the cosine ratio to calculate the length of t.
R
t
S
s=15 cm
r
40o
T
2
Example 2
Use the cosine ratio to calculate the
measure of B.
B
a
C
c = 10 cm
b = 8 cm
A
3
Example 3
Application
A ladder leans against a vertical wall and makes an angle of 65o with the ground. The foot of the ladder is 2 m from the base of the wall. Calculate the length of the ladder, to the nearest tenth of a metre.
4

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