For the simple rightangled triangle below, the tangent of the angle θ, is the ratio of the opposite side, o, to the adjacent side, a.
i.e. for the triangle above,
The Excel TAN function calculates the tangent of a given angle (which is supplied in radians).
The format of the function is :
Where the number argument is the angle, in radians, that you want to calculate the tangent 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.
The easiest way to do this is to use the Excel Radians function:
Column B of the spreadsheet below, shows examples of the Excel Tan Function, used to calculate the tangent of different angles, which are in either degrees or radians.
Formulas:

Results:

Further information and examples of the Excel Tan function can be found on the Microsoft Office website.