Cosine FunctionMath Trig Complex Class

```Public Function Cosine( _
ByVal vX As Variant _
) As Variant```

Cosine of a complex or real number. Inverse of the ACos function.

Plot:
`    For X = -8 to 8 step .1:`
```       *****               ****               *****
**   *              ** |**              *   **
*     *            **  | **            *     *
*      **           *   |  *           **      *
*       *          *    |   *          *       *
*        *          *    |   *          *        *
*---------*--------*-----+----*--------*---------*
**       *     |    *       **
*      *      |     *      *
*     *      |     *     *
**   *       |      *   **
****        |       ****```

Examples:
```    Cosine(-0.5) = 0.877582561890373
Cosine(0) = 1
Cosine(0.5) = 0.877582561890373
Cosine(1) = 0.54030230586814
Cosine(1.5) = 7.07372016677029E-02
Cosine(2) = -0.416146836547142
Cosine(2.5) = -0.801143615546934
Cosine(3) = -0.989992496600445
Cosine(3.5) = -0.936456687290796
Cosine("2.3|-4.5") = "-29.9918288739746|33.5589799796873"```
See also:
```    Sine Function
Tangent Function
Cosecant Function
ACos Function
CosH Function
Cos Function (Visual Basic)```
vX: Number whose cosine is returned. Function returns Null if vX is Null or cannot be fixed up to a real or complex number (as defined by the ComplexStringToReals function). Complex numbers are represented within strings as "R|I" where R is the real part and I is the imaginary part.
Return: The result is expressed in radians.

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