# Power Pivot Principles: The A to Z of DAX Functions – ATAN

21 September 2021

*In our long-established Power Pivot Principles articles, we are starting a new series on the A to Z of Data Analysis eXpression (DAX) functions. This week it’s ATAN without colour …*

*The ATAN function*

This function returns the principal value of the arctangent (inverse tangent) of a number (which is not the same as the reciprocal of the tangent). This needs some explanation. Consider a right-angled triangle:

Using the age-old mathematics mnemonic **SOHCAHTOA**, we get:

**sin x**= opposite / longest side (hypotenuse) = O/H**cos x**= adjacent / hypotenuse = A/H**tan x**= opposite / adjacent = O/A**arctan y**=**tan**is the angle whose tangent is^{-1}y**y**.

This may be charted as follows:

The arctangent is the angle whose tangent is number. The returned angle is given in radians in the range **(-pi/2)** to **(pi/2)**.

The syntax is very simple:

**=ATAN (number)**

It has only one argument:

**number:**the tangent of the angle you want.

Please see my example below:

If you want to convert the result from radians to degrees, simply multiply it by 180/**PI ()** or use the **DEGREES** function.

The example is shown below:

Again, this is straightforward.

*Come back next week for our next post on Power Pivot in the **Blog** section. In the meantime, please remember we have training in Power Pivot which you can find out more about **here**. If you wish to catch up on past articles in the meantime, you can find all of our Past Power Pivot blogs **here**.*