Variables can represent any number. However, since you do not know what number it could or does represent, you have to treat it differently than numbers because it is a variable. Algebra deals with many different aspects using Variables. In algebra, you learn to simplify expressions involving variables and also you deal with graphs of equations involving variables. Variables are usually represented by a single letter.
Variables can be added, subtracted, divided, and multiplied, similar to numbers but with a twist.
Addition between variables can be technically done, meaning that you can do "X + Y" but you will end up with "X + Y". You cannot literally combine a number with a variable (unless you are talking about multiplication such as 3 times X which would be represented by 3X). Therefore if you are trying to add "3" to "X" you would get "3 + X". If you were to then want to add 7 to "3+X" then you would add together the two like terms, in this case they are both numbers. The resultant would be calculated like " '3+7' + X" = "10 + X". Let's say, instead of adding 7 we wanted to add "X" to "3+X". Once again, you would combine the like terms, the two X's, which would result in "3 + 2X". When you have a variable and a number being added or subtracted the combination of the two is generally called a Binomial. That means that "10 + X" is considered a binomial. So in a general definition a Binomial is a set where a single variable is being added to some number (which includes negative numbers). Binomials are in further detail in other sections. Subtraction is handled in a similar way for variables and numbers.
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