Why are certain variables used when referring to certain types of numbers.

Question

When referring to a real number people normally use the variable $x$, when people refer to complex numbers they normally use the variable $z$, and when people refer to matrices they normally name the first one $A$. Is the a reason or rule people do this one is it just a habit? I know matrices have to be reffered to as a capitol letter but why normally $A$? And why $x$ for real numbers and $z$ for complex ones? Why do people do this? Please edit my tags if I am using the wrong ones, do not know which tags to use.

Answer 1

As the comments say it is mostly customary and make math easier to read when everyone has the same "habits".

For the real number $x$ that is very interesting, but I found something online that is equally interesting (maybe not useful or incorrect, whose to say)

"In the 2012 TED Talk above, Terry Moore traces the use of the letter $x$ in algebra to the Arabic word al-shalan, which means "the unknown thing," claiming that, in translations of the writing of Arabic mathematicians, that word became linked to the Greek letter chi and then reached us through Latin ... "

For complex numbers, it is because each complex number has a real part and imaginary part both are real numbers. So the first is denoted $x$ because it is unknown and real, and the second is usually denoted $y$ because it is easy to read and remember. And what comes next in the alphabet is $z$, hence the common notation is $z=x+iy$

For matrices, it is capital to differentiate it from scalars visually, and my best guess is that in mathematics we don't have a lot of things commonly denoted $A,B,C,D,E,...$. So it is convenient to denote matrices like this and minimize visual confusion