Learned from Google, Wikipedia, various websites, actual books and periodicals, and other forms of media.

• Why "x" is the most popular variable. From wikipedia, I found that:
  • The use of variables (actually replacing values with letters) aren't developed not until several hundreds of years ago. Arabic algebra made use of full texts in mathematics; the variable quantity was denoted in an Arabic word which, pronounced in Old Spanish, is "sei" and written as "xei." Out of habit, the word was abbreviated to x.
  • Aside from this historical theory, "x" is also commonly believed to mean "unknown" or "secret," as in project X or mister X.
• Where the f-word came from.
  • Told by my friend Meme who learned it from a professor, it is said to originate from the acronym "Fornication Under the Consent of the King," as in the olden days, due to population issues, permission should be given by the king before anyone can have sex.
  • Somehow, the above theory was disputed by an online reference. The acronym is a false urban legend. The accepted etymology of the word is that from native Germanic words which mean "striking, rubbing, and having sex."
  • John le Fucker? WRONG.