For the simple rightangled triangle below, the cosine of the angle θ, is the ratio of the adjacent side, a, to the hypotenuse, h.
I.e. for the triangle above,
The Excel COS function calculates the cosine of a given angle.
The syntax of the function is:
Where the number argument is the angle, in radians, that you want to calculate the cosine of.
Converting from Radians to Degrees
If your angle is in degrees, you will need to convert it into radians before supplying it to the Cos function.
This can be done by using the Excel Radians function:
The following spreadsheet shows the Excel Cos Function, used to calculate the cosine of four different angles.
Formulas:

Results:

Note that in the above examples:
For further information and examples of the Excel Cos function, see the Microsoft Office website.