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Cosine
Definition Of Cosine
In a right-angles triangle Cosine is the ratio of length of the adjacent side to the length of the hypotenuse.
More About Cosine
Cosine is also written as cos.
Example of Cosine
cos θ = 
& cos θ = 4/5
Video Examples: Sine and Cosine Rule 1 (GCSE Higher Maths)
Solved Example on Cosine
Ques: If x = 8 units, y = 15 units, and a = 17 units, then find the value of cos C in the right triangle ABC.
Choices:
A. 15/17
B. 17/18
C. 17/15
D. 8/17
Correct Answer: D
Solution:
Step 1: Cos C = 
Step 2: In â–³ABC, the adjacent side of C is 
and the hypotenuse is
.
Step 3: So, Cos C = 
Step 4: = 8/17 [Substitute BC = 8 and AC = 17.]