Cosine function, cos(x)

cos(x), cosine function.

Cosine definition

In a right triangle ABC the sine of α, sin(α) is defined as the ratio betwween the side adjacent to angle α and the side opposite to the right angle (hypotenuse):

cos α = b / c

For example:

b = 5″
c = 10″
cos α = b / c = 5 / 10 = 0.5

TBD

Inverse cosine function

The arccosine of x is defined as the inverse cosine function of x when -1≤x≤1.

When the cosine of y is equal to x:

cos y = x