# Why do we use "X" in mathematics as an unknown variable?

Have you ever noticed why we use X as an unknown variable in solving equations?In algebra, we solve equations and most of the time we are asked to find the value of X when there is one unknown variable. When there is more than one variable we use letters Y and Z. Why is it so why don't we use A, B or any other letter. Have you thought of it ever?

What's the reason or logic behind it?.