* Fixed typos and changed OO to OOP
Some typos, mainly to ease the reading for Portuguese people.
Changed every OO to OOP because it was confusing, and calling it OOP like every other language calls it, makes it even easier for begginers to search online more information about the subject.
* Fixed the sentence that should be in PT-BR
Changed "porquê" to "por que" because is correct in PT-BR
Intermediate code solution doesn't pass tests when the greater number is even because it's the starting acc without passing the reducer function that avoids even number.
Proposed solution: reverse the array before reduce.
Fixed copy/pasting(?) typos, also changed the 'because' in each example to explain the why instead of just showing it's true for a single number, not mentioning any others. (Proof by example is very, very, VERY bad to encourage.)
Presented formula, derived it and gave examples, one simple and one more involved to show how it's not always 'easy' or 'obvious' how this rule can be applied to help, a rule of thumb in how to use it and a brief list of generalizations.
* [x] I have read [freeCodeCamp's contribution guidelines](https://github.com/freeCodeCamp/freeCodeCamp/blob/master/CONTRIBUTING.md).
* [x] My pull request has a descriptive title (not a vague title like `Update index.md`)
* [x] My pull request targets the `master` branch of freeCodeCamp.
* [x] None of my changes are plagiarized from another source without proper attribution.
* [x] My article does not contain shortened URLs or affiliate links.
If your pull request closes a GitHub issue, replace the XXXXX below with the issue number.
Closes #XXXXX
* fixing #24573
fixing #24573 - Guide: Let and Const - Unwanted underscores in search result and incorrect URL
- changed underscore to hyphen, same problem was also happening with arrow_functions
https://github.com/freeCodeCamp/freeCodeCamp/issues/24573
* fix: added 3 backticks for code sections
