# Function Reference

# ACos

Calculates the arcCosine of a number.

ACos ( expression )

## Parameters

expression | Any value between -1 and 1 inclusive.

## Return Value

Returns the trigonometric arccosine of the number. Result is in radians.

## Remarks

ACos(x) is mathematically defined only for -1 < x < 1, so ACos() tends to return -1.#IND for other values of x.

## Related

ASin, ATan, Cos, Sin, Tan

## Example

### Example 1

    #include <MsgBoxConstants.au3>

    Example()

    Func Example()
        ; Assign a Local variable the arcCosine of 0.5.
        Local $fArcCos1 = ACos(0.5)

        ; Display the result.
        MsgBox($MB_SYSTEMMODAL, "", $fArcCos1 & " rad.")

        ; Assign a Local constant variable the approximate PI number.
        Local Const $PI = 3.141592653589793

        ; Assign a Local variable the formula to switch from radian to degree (equals to one radian in degree).
        Local $fRadToDeg = 180 / $PI

        ; Assign a Local variable a number in degree.
        Local $fArcCos2 = $fRadToDeg * ACos(-1)

        ; Display the result.
        MsgBox($MB_SYSTEMMODAL, "", $fArcCos2 & " deg.")
    EndFunc   ;==>Example

### Example 2

    ; Example of using ACos with degrees.

    #include <Math.au3>
    #include <MsgBoxConstants.au3>

    Local $fDegree = _Degree(ACos(-1))

    MsgBox($MB_SYSTEMMODAL, Default, "ACos(-1) = " & $fDegree & " degrees")