docs: adds TANH documentation page

docs/src/functions/math_and_trigonometry/tanh.md

@@ -3,9 +3,37 @@ layout: doc
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 lang: en-US
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+# TANH function
+## Overview
+TANH is a function of the Math and Trigonometry category that calculates the hyperbolic tangent of a number.
+## Usage
+### Syntax
+**TANH(<span title="Number" style="color:#1E88E5">number</span>) => <span title="Number" style="color:#1E88E5">tanh</span>**
+### Argument descriptions
+* *number* ([number](/features/value-types#numbers), required). The hyperbolic angle whose hyperbolic tangent is to be calculated, expressed in radians.
+### Additional guidance
+The formula for the hyperbolic tangent is:
+$$
+\text{tanh(x)} = \dfrac{sinh(x)}{cosh(x)} = \dfrac{e^x-e^{-x}}{e^x+e^{-x}}
+$$
+### Returned value
+TANH returns a real [number](/features/value-types#numbers) in the range (-1,+1) that is the hyperbolic tangent of the specified hyperbolic angle.
+### Error conditions
+* In common with many other IronCalc functions, TANH propagates errors that are found in its argument.
+* If no argument, or more than one argument, is supplied, then TANH returns the [`#ERROR!`](/features/error-types.md#error) error.
+* If the value of the *number* argument is not (or cannot be converted to) a [number](/features/value-types#numbers), then TANH returns the [`#VALUE!`](/features/error-types.md#value) error.
+* For some argument values, TANH may return a [`#DIV/0!`](/features/error-types.md#div-0) error.
+<!--@include: ../markdown-snippets/error-type-details.txt-->
+## Details
+* The TANH function utilizes the *tanh()* method provided by the [Rust Standard Library](https://doc.rust-lang.org/std/).
+* The figure below illustrates the TANH function.
+<center><img src="/functions/images/hyperbolictangent-curve.png" width="350" alt="Graph showing tanh(x)."></center>
 
-# TANH
+## Examples
+[See some examples in IronCalc](https://app.ironcalc.com/?example=tanh).
 
-::: warning
-🚧 This function is implemented but currently lacks detailed documentation. For guidance, you may refer to the equivalent functionality in [Microsoft Excel documentation](https://support.microsoft.com/en-us/office/excel-functions-by-category-5f91f4e9-7b42-46d2-9bd1-63f26a86c0eb).
-:::
+## Links
+* For more information about hyperbolic functions, visit Wikipedia's [Hyperbolic functions](https://en.wikipedia.org/wiki/Hyperbolic_functions) page.
+* See also IronCalc's [SINH](/functions/math_and_trigonometry/sinh), [COSH](/functions/math_and_trigonometry/cosh) and [TAN](/functions/math_and_trigonometry/tan) functions.
+* Visit Microsoft Excel's [TANH function](https://support.microsoft.com/en-us/office/tanh-function-017222f0-a0c3-4f69-9787-b3202295dc6c) page.
+* Both [Google Sheets](https://support.google.com/docs/answer/3093755) and [LibreOffice Calc](https://wiki.documentfoundation.org/Documentation/Calc_Functions/TANH) provide versions of the TANH function.