The Excel COS Function
Cosine of an Angle
For the simple right-angled 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 trig. ratios are discussed further on the
Wikipedia Trigonometric Ratios Page
The Excel COS function calculates the cosine of a given angle.
The format of the function is :
COS( number )
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.
The easiest way to do this is to use the
Excel Radians function:
=RADIANS( degrees )
An example of this is given below.
Cos Function Examples
Column A of the spreadsheet below, shows examples of the Excel Cos Function, used to calculate the
cosine of different angles.
||=COS( 0.785398163 )
|| - cos of 0.785398163 Radians
||=COS( 0 )
|| - cos of 0 Radians
||=COS( -PI()/3 )
|| - cos of -π/3 Radians
||=COS( RADIANS( -30 ) )
|| - cos of -30 Degrees
Note that in the above examples:
- In cell A3, the Excel Pi function is
used to supply the value -π/3;
- In cell A4, the Excel Radians function
is used to convert the angle of -30 degrees into radians before it is supplied to the Cos function.
Further information and examples of the Excel Cos function can be found on the
Microsoft Office website.