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

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The `Math.Cos()` function returns the cosine of the specified angle in radians in the range `-1` to `+1`.

``````using System;

class Program
{
static void Main(string[] args)
{
Console.WriteLine( Math.Cos( 0                  ) ); //   1 <-     0 degrees
Console.WriteLine( Math.Cos( 1.5707963267948966 ) ); //  ~0 <-  ~90 degrees ==  PI / 2
Console.WriteLine( Math.Cos( 3.1415926535897932 ) ); // ~-1 <- ~180 degrees ==  PI
Console.WriteLine( Math.Cos( 4.71238898038469   ) ); //  ~0 <- ~270 degrees == -PI * (3 / 2)
Console.WriteLine( Math.Cos( 6.2831853071795850 ) ); //  ~1 <- ~360 degrees ==  PI * 2

Console.WriteLine( Math.Cos( -1.5707963267948966) ); //  ~0 <- ~-90 degrees == -PI / 2
}
}``````

Note: `6.123233995736766e-17`, `-1.8369701987210297e-16` and `6.123233995736766e-17` should be equal to `0` but they are not because of computation precision error.

## 1. Documentation

 Syntax ``````namespace System { public final class Math { // ... public static double Cos(double number) { ... } // ... } }`````` Parameters `number` - double value in radians (primitive value). Result returns a numeric value between `-1` and `+1`, which represents the cosine of the angle (primitive value). Description `Cos` is a static method that takes only one parameter and returns an approximation of `cos(x)` mathematical function result.

``````using System;

class Program
{
static void Main(string[] args)
{
double x1 = 0.0;          // beginning of calculation in radians
double x2 = Math.PI / 2;  // ending of calculation radians

double dx = Math.PI / 9; // calculation step in degrees

{

}
}
}``````

Output:

``````cos(0.0 rad) = 1

## 3. Working with degrees

``````using System;

class Program
{
static double calculateCos(double deg)
{
double rad = (Math.PI / 180) * deg;

}

static void Main(string[] args)
{
double x1 = 0.0;  // beginning of calculation in degrees
double x2 = 90.0; // ending of calculation degrees

double dx = 15.0;  // calculation step in degrees

for (double deg = x1; deg <= x2; deg += dx)
{
double y = calculateCos(deg);

Console.WriteLine("cos(" + deg + " deg) = " + y);
}
}
}``````

Output:

``````cos(0.0 deg) = 1
cos(15.0 deg) = 0.9659258262890683
cos(30.0 deg) = 0.8660254037844387
cos(45.0 deg) = 0.7071067811865476
cos(60.0 deg) = 0.5000000000000001
cos(75.0 deg) = 0.25881904510252074
cos(90.0 deg) = 6.123233995736766E-17``````

## 4. Reversed console plot example

``````using System;
using System.Text;

class Program
{
static void Main(string[] args)
{
double x1 = 0.0;      // beginning of cosine chart
double x2 = 3 * 3.14; // end of cosine chart

double dx = 3.14 / 4.0; // x axis step
double dy = 1.0  / 5.0; // y axis step

{
double y1 = 0.0;
double y2 = Math.Cos(rad) + 1;

StringBuilder line = new StringBuilder();

for (double y = y1; y < y2; y += dy)
{
line.Append(" ");
}
Console.WriteLine(line.Append("+"));
}
}
}``````

Output:

``````           +
+
+
+
+
+
+
+
+
+
+
+``````

## References

1. Cosine - Wikipedia

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