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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)

public static double Acos(
	double 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.

	/// <summary> 
	/// The following class represents simple functionality of the trapezoid. 
	/// </summary> 
	class MathTrapezoidSample
	{
		private double m_longBase;
		private double m_shortBase;
		private double m_leftLeg;
		private double m_rightLeg;

		public MathTrapezoidSample(double longbase, double shortbase, double leftLeg, double rightLeg)
		{
			m_longBase = Math.Abs(longbase);
			m_shortBase = Math.Abs(shortbase);
			m_leftLeg = Math.Abs(leftLeg);
			m_rightLeg = Math.Abs(rightLeg);
		}

		private double GetRightSmallBase()
		{
			return (Math.Pow(m_rightLeg,2.0) - Math.Pow(m_leftLeg,2.0) + Math.Pow(m_longBase,2.0) + Math.Pow(m_shortBase,2.0) - 2* m_shortBase * m_longBase)/ (2*(m_longBase - m_shortBase));
		}

		public double GetHeight()
		{
			double x = GetRightSmallBase();
			return Math.Sqrt(Math.Pow(m_rightLeg,2.0) - Math.Pow(x,2.0));
		}

		public double GetSquare()
		{
			return GetHeight() * m_longBase / 2.0;
		}

		public double GetLeftBaseRadianAngle()
		{
			double sinX = GetHeight()/m_leftLeg;
			return Math.Round(Math.Asin(sinX),2);
		}

		public double GetRightBaseRadianAngle()
		{
			double x = GetRightSmallBase();
			double cosX = (Math.Pow(m_rightLeg,2.0) + Math.Pow(x,2.0) - Math.Pow(GetHeight(),2.0))/(2*x*m_rightLeg);
			return Math.Round(Math.Acos(cosX),2);
		}

		public double GetLeftBaseDegreeAngle()
		{
			double x = GetLeftBaseRadianAngle() * 180/ Math.PI;
			return Math.Round(x,2);
		}

		public double GetRightBaseDegreeAngle()
		{
			double x = GetRightBaseRadianAngle() * 180/ Math.PI;
			return Math.Round(x,2);
		}

		static void Main(string[] args)
		{
			MathTrapezoidSample trpz = new MathTrapezoidSample(20.0, 10.0, 8.0, 6.0);
			Console.WriteLine("The trapezoid's bases are 20.0 and 10.0, the trapezoid's legs are 8.0 and 6.0");
			double h = trpz.GetHeight();
			Console.WriteLine("Trapezoid height is: " + h.ToString());
			double dxR = trpz.GetLeftBaseRadianAngle();
			Console.WriteLine("Trapezoid left base angle is: " + dxR.ToString() + " Radians");
			double dyR = trpz.GetRightBaseRadianAngle();
			Console.WriteLine("Trapezoid right base angle is: " + dyR.ToString() + " Radians");
			double dxD = trpz.GetLeftBaseDegreeAngle();
			Console.WriteLine("Trapezoid left base angle is: " + dxD.ToString() + " Degrees");
			double dyD = trpz.GetRightBaseDegreeAngle();
			Console.WriteLine("Trapezoid left base angle is: " + dyD.ToString() + " Degrees");
		}
	}

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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