In order to write mathematical formulas with symbols and express them concisely. Vader, a French mathematician, is the Vader who put forward the relationship between root and coefficient in junior middle school mathematics by Vieta theorem (he is a lawyer, a member of parliament, and studies mathematics as an amateur, just like Fermat). He first proposed to use consonant letters, such as B.C., to represent known quantities, and vowel letter A to represent unknown quantities. However, in the process of use, it is very inconvenient to judge whether it is a consonant or a vowel every time. It's best to describe it in words. Later, Descartes, a great mathematician who invented rectangular coordinate system, optimized the expression. The front letter abc means known, and the back letter XYZ means unknown, which is clear at a glance, simplifying the symbol record. Later, it was accepted and used by mathematicians and has continued to this day.

Everything happens for a reason, and you can't act rashly with regulations.