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Math.Acos Method

Updated: April 2011

Returns the angle whose cosine is the specified number.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Shared Function Acos ( _
	d As Double _
) As Double
'Usage
Dim d As Double 
Dim returnValue As Double 

returnValue = Math.Acos(d)

Parameters

d
Type: System.Double

A number representing a cosine, where d must be greater than or equal to -1, but less than or equal to 1.

Return Value

Type: System.Double
An angle, θ, measured in radians, such that 0 θ π
-or-
NaN if d < -1 or d > 1 or d equals NaN.

Multiply the return value by 180/Math.PI to convert from radians to degrees.

The following code sample uses the Acos method to assist in the computation of the inner angles of a given trapezoid.

'The following class represents simple functionality of the trapezoid. 
Class MathTrapezoidSample

    Private m_longBase As Double 
    Private m_shortBase As Double 
    Private m_leftLeg As Double 
    Private m_rightLeg As Double 

    Public Sub New(ByVal longbase As Double, ByVal shortbase As Double, ByVal leftLeg As Double, ByVal rightLeg As Double)
        m_longBase = Math.Abs(longbase)
        m_shortBase = Math.Abs(shortbase)
        m_leftLeg = Math.Abs(leftLeg)
        m_rightLeg = Math.Abs(rightLeg)
    End Sub 

    Private Function GetRightSmallBase() As Double
        GetRightSmallBase = (Math.Pow(m_rightLeg, 2) - Math.Pow(m_leftLeg, 2) + Math.Pow(m_longBase, 2) + Math.Pow(m_shortBase, 2) - 2 * m_shortBase * m_longBase) / (2 * (m_longBase - m_shortBase))
    End Function 

    Public Function GetHeight() As Double 
        Dim x As Double = GetRightSmallBase()
        GetHeight = Math.Sqrt(Math.Pow(m_rightLeg, 2) - Math.Pow(x, 2))
    End Function 

    Public Function GetSquare() As Double
        GetSquare = GetHeight() * m_longBase / 2
    End Function 

    Public Function GetLeftBaseRadianAngle() As Double 
        Dim sinX As Double = GetHeight() / m_leftLeg
        GetLeftBaseRadianAngle = Math.Round(Math.Asin(sinX), 2)
    End Function 

    Public Function GetRightBaseRadianAngle() As Double 
        Dim x As Double = GetRightSmallBase()
        Dim cosX As Double = (Math.Pow(m_rightLeg, 2) + Math.Pow(x, 2) - Math.Pow(GetHeight(), 2)) / (2 * x * m_rightLeg)
        GetRightBaseRadianAngle = Math.Round(Math.Acos(cosX), 2)
    End Function 

    Public Function GetLeftBaseDegreeAngle() As Double 
        Dim x As Double = GetLeftBaseRadianAngle() * 180 / Math.PI
        GetLeftBaseDegreeAngle = Math.Round(x, 2)
    End Function 

    Public Function GetRightBaseDegreeAngle() As Double 
        Dim x As Double = GetRightBaseRadianAngle() * 180 / Math.PI
        GetRightBaseDegreeAngle = Math.Round(x, 2)
    End Function 

    Public Shared Sub Main()
        Dim trpz As MathTrapezoidSample = New MathTrapezoidSample(20, 10, 8, 6)
        Console.WriteLine("The trapezoid's bases are 20.0 and 10.0, the trapezoid's legs are 8.0 and 6.0")
        Dim h As Double = trpz.GetHeight()
        Console.WriteLine("Trapezoid height is: " + h.ToString())
        Dim dxR As Double = trpz.GetLeftBaseRadianAngle()
        Console.WriteLine("Trapezoid left base angle is: " + dxR.ToString() + " Radians")
        Dim dyR As Double = trpz.GetRightBaseRadianAngle()
        Console.WriteLine("Trapezoid right base angle is: " + dyR.ToString() + " Radians")
        Dim dxD As Double = trpz.GetLeftBaseDegreeAngle()
        Console.WriteLine("Trapezoid left base angle is: " + dxD.ToString() + " Degrees")
        Dim dyD As Double = trpz.GetRightBaseDegreeAngle()
        Console.WriteLine("Trapezoid left base angle is: " + dyD.ToString() + " Degrees")
    End Sub 

End Class

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

April 2011

Updated return value information.

Customer feedback.

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