After beginning to learn about thetalogy, you may wonder: What's the difference between theta and X—or any unknown variable? There are a few important differences between the two.
First, theta is always a positive, finite number. X can be equal to any number, negative or positive (except for infinity, algebra doesn't allow it). So while theta can equal any number above zero and below infinity, X can equal any number between negative and positive infinity, including zero.
The second main difference between theta and X, is that X is a variable and theta is not. While X can equal any number, it only equals one number at a time. X is any of the numbers, and theta is all of the numbers in its range, at the same time. Theta is basically a set of numbers; it equals all positive numbers collectively.
In conclusion, while X and theta may seem similar, they are clearly different because one, theta cannot equal zero or any negative number, and two, theta is not a variable.