__See Also__ __Example__

Returns the arctangent of a number.

**Syntax**

**Atn(***number***)**

**Remarks**

The argument *number* can be any valid __numeric expression__ .

The **Atn** function takes the ratio (*number*) of two sides of a right triangle and returns the corresponding angle. The ratio is the length of the side opposite the angle divided by the length of the side adjacent to the angle.

The result is expressed in radians and is in the range **-**Pi/2 to Pi/2 radians. Pi is approximately 3.141593.

To convert degrees to radians, multiply degrees by Pi/180. To convert radians to degrees, multiply radians by 180/Pi.

**Note Atn** is the inverse trigonometric function of **Tan**, which takes an angle as its argument and returns the ratio of two sides of a right triangle. Do not confuse **Atn** with the cotangent, which is the simple inverse of a tangent (1/tangent).

__Cos____ Function__

__Sin____ Function__

__Tan____ Function__

__Math Functions__

__Derived Math Functions__

The example uses **Atn** to calculate Pi. By definition, Atn(1) is 45 degrees; 180 degrees equals Pi radians. To try this example, paste the code into the Declarations section of a form. Then press F5 and click the form.

Sub Form_Click ()

Dim Msg, Pi ' Declare variables.

Pi = 4 * Atn(1) ' Calculate Pi.

Msg = "Pi is equal to " & Pi

MsgBox Msg ' Display results.

End Sub