cos alpha α = a/c
α = angle alpha
a = side "a"
b = side "b"
c = side "c"
Let's assume we have a right triangle ABC, where ∠C=90o. Side a is adjacent to angle alpha, side b is opposite to angle alpha, and c is the hypotenuse (the longest side of the triangle).
The definition of the cosine of angle α is:
For this example:
Assume the side lengths are:
a2 + b2 = c2
32 + 42 = 52
9 + 16 = 25
Since the equality holds, it is a right triangle.
Result:
Thus, the cosine of angle α in this right triangle is 0.6.