To get the link
https://en.wikipedia.org/wiki/Variable_(mathematics)#Genesis_and_evolution_of_the_concept
use the following code in your comment:

[https://en.wikipedia.org/wiki/Variable\_(mathematics)#Genesis\_and\_evolution\_of\_the\_concept](https://en.wikipedia.org/wiki/Variable_(mathematics\)#Genesis_and_evolution_of_the_concept)

See Comment formatting/Escaping special symbols on the wiki for more details (I've backslash-escaped underscores _ in the text part of the link to avoid their turning surrounding texts into italics, and the closing round bracket in the URL part of the link to avoid its interpretation as the end of the URL).