# Math.Asin Method

.NET Framework 4.5

Returns the angle whose sine is the specified number.

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

## Syntax

```public static double Asin(
double d
)
```

#### Parameters

d
Type: System.Double

A number representing a sine, 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 -π/2 θ π/2
-or-
NaN if d < -1 or d > 1 or d equals NaN.

## Remarks

A positive return value represents a counterclockwise angle from the x-axis; a negative return value represents a clockwise angle.

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

## Examples

The following example uses Asin to assist in the computation of the inner angles of a given trapezoid.

```/// <summary>
/// The following class represents simple functionality of the trapezoid.
/// </summary>
using System;

namespace MathClassCS
{
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;
}

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

{
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");
}
}
}
```

## Version Information

#### .NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

#### .NET Framework Client Profile

Supported in: 4, 3.5 SP1

#### Portable Class Library

Supported in: Portable Class Library

#### .NET for Windows Store apps

Supported in: Windows 8

#### .NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

## Platforms

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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