[Term Entry] C# Math-functions: SinCos() (#7970)

* [Term Entry] C# Math-functions: SinCos()

Added documentation for the Math.SinCos() method which returns both
the sine and cosine of a given angle as a tuple. This method is more
efficient than calling Math.Sin() and Math.Cos() separately.

Resolves #7953

* minor content fixes

* wrong hyperlink for the c sharp lang

---------

Author: ylevental

content/c-sharp/concepts/math-functions/terms/sincos/sincos.md

@@ -0,0 +1,90 @@
+---
+Title: '.SinCos()'
+Description: 'Returns both the sine and cosine of a given angle.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+Tags:
+  - 'Arithmetic'
+  - 'Functions'
+  - 'Methods'
+  - 'Numbers'
+CatalogContent:
+  - 'learn-c-sharp'
+  - 'paths/computer-science'
+---
+
+The **`Math.SinCos()`** method returns both the sine and cosine of a specified angle (in radians) as a tuple.
+
+## Syntax
+
+```pseudo
+Math.SinCos(angle);
+```
+
+**Parameters:**
+
+- `angle`: A double-precision floating-point number representing an angle in radians.
+
+**Return value:**
+
+The method returns a tuple containing both the sine and cosine of the `angle` as `double` values. If the value of `angle` equals `NaN`, `NegativeInfinity`, or `PositiveInfinity`, the method returns `NaN` for both values.
+
+> **Note:** This method is more efficient than calling `Math.Sin()` and `Math.Cos()` separately when both values are needed.
+
+## Example 1
+
+In this example, the code converts 45 degrees to radians and uses the `Math.SinCos()` method to return both the sine and cosine of that angle:
+
+```cs
+using System;
+
+public class Example {
+  public static void Main(string[] args) {
+    double degrees = 45;
+    double radians = degrees * Math.PI/180;
+
+    var (sine, cosine) = Math.SinCos(radians);
+
+    Console.WriteLine("The sine of " + degrees + " degrees is: " + sine);
+    Console.WriteLine("The cosine of " + degrees + " degrees is: " + cosine);
+  }
+}
+```
+
+The example will result in the following output:
+
+```shell
+The sine of 45 degrees is: 0.7071067811865476
+The cosine of 45 degrees is: 0.7071067811865476
+```
+
+## Example 2
+
+In this example, both sine and cosine values of a 30° angle are calculated using `Math.SinCos()`:
+
+```cs
+using System;
+
+public class Example {
+
+  public static void Main(string[] args) {
+    // Angle in degrees
+    double angle = 30;
+
+    var (sine, cosine) = Math.SinCos(angle * Math.PI/180);
+
+    Console.WriteLine("The sine of " + angle + " degrees is: " + sine);
+    Console.WriteLine("The cosine of " + angle + " degrees is: " + cosine);
+  }
+}
+```
+
+The output of this code is:
+
+```shell
+The sine of 30 degrees is: 0.5
+The cosine of 30 degrees is: 0.8660254037844386
+```
+
+> **Note:** The `Math.SinCos()` method is supported starting from .NET 6 and later. It is not available in earlier .NET versions.