and is abbreviated to cos. For a given angle Ɵ, cosƟ = adjacent ÷ hypotenuse. This is written as a fraction. Image caption, The opposite divided by the adjacent for each triangle is 3/4 or 6/8.

An inverse function takes the output and does the opposite to get back to the input. The cosine (cos) function takes the angle Ɵ and gives the answer to adjacent ÷ hypotenuse (in this example, ...