# Atn Function

The arctangent is the inverse of the tangent function. The Atn Function returns the angle "Alpha", expressed in radians, using the tangent of this angle. The function can also return the angle "Alpha" by comparing the ratio of the length of the side that is opposite of the angle to the length of the side that is adjacent to the angle in a right-angled triangle.

Atn(side opposite the angle/side adjacent to angle)= Alpha

### Syntax:

``````
Atn (Number As Double) As Double
``````

Double

### Parameters:

Number: Any numerical expression that represents the ratio of two sides of a right triangle. The Atn function returns the corresponding angle in radians (arctangent).

Pi is here the fixed circle constant with the rounded value 3.14159. Pi is a Basic mathematical constant.

5 無效的程序呼叫

### Example:

``````
REM 以下示例用於直角三角形的計算
REM 依 Alpha 角的正切值來計算 Alpha 角：
Sub ExampleAtn
REM 捨入後的 PI = 3.1415926 是預先定義的常數
Dim d1 As Double
Dim d2 As Double
d1 = InputBox("Enter the length of the side adjacent to the angle:","Adjacent")
d2 = InputBox("Enter the length of the side opposite the angle:","Opposite")
Print "The Alpha angle is"; (atn (d2/d1) * 180 / Pi); " degrees"
End Sub
``````