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# C# / .NET - Math.Asin() method example

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The `Math.Asin` function returns number in radians in the range `-Math.PI/2` to `+Math.PI/2`. The function calculates the inverted sine function value.

``````using System;

public class Program
{
static double CalculateAngle(double a, double h)
{
return Math.Asin(a / h);
}

public static void Main(string[] args)
{
/*
|\
| \ h
a |  \
|__*\ <- angle
b
*/

double a, b, h;

// a, b and h build isosceles right triangle
a = 3;
b = a;
h = Math.Sqrt(a * a + b * b);
Console.WriteLine( CalculateAngle(a, h) ); // 0.7853981633974483 <- ~45 degrees

// a, b and h build half of equilateral triangle
a = 3;
b = a * Math.Sqrt(3);
h = Math.Sqrt(a * a + b * b);
Console.WriteLine( CalculateAngle(a, h) ); // 0.5235987755982989 <- ~30 degrees

// a, b and h are not able to build triangle
a = 3;
b = a;
h = 1;
Console.WriteLine( CalculateAngle(a, h) ); // NaN
}
}``````

## 1. Documentation

 Syntax ``````namespace System { public static class Math { // ... public static double Asin(double number) { ... } // ... } }`````` Parameters `number` - double value that represents the result of the operation `adjacent / hypotenuse` on the right triangle (primitive value). `number` should be in the range `-1` to `+1`. Result `number` value in radians in the range `-Math.PI/2` to `+Math.PI/2` (primitive value). If the value can not be calculated `NaN` is returned. Description `Asin` is a static method that takes only one parameter and returns an approximation of the result of the mathematical function arcsine(x).

## 2. Working with degrees

``````using System;

public class Program
{
static double CalculateAngle(double a, double h)
{
double angle = Math.Asin(a / h);

return (180 / Math.PI) * angle; // rad to deg conversion
}

public static void Main(string[] args)
{
/*
|\
| \ h
a |  \
|__*\ <- angle
b
*/

double a, b, h;

// a, b and h build isosceles right triangle
a = 3;
b = a;
h = Math.Sqrt(a * a + b * b);
Console.WriteLine(  CalculateAngle(a, h)); // ~45 degrees

// a, b and h build half of equilateral triangle
a = 3;
b = a * Math.Sqrt(3);
h = Math.Sqrt(a * a + b * b);
Console.WriteLine(  CalculateAngle(a, h)); // ~30 degrees

// a, b and h are not able to build triangle
a = 3;
b = a;
h = 1;
Console.WriteLine(  CalculateAngle(a, h)); // NaN
}
}``````

## References

1. Inverse trigonometric functions - Wikipedia

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