# Plus and Minus (Different Variables)

Theory

### DifferentVariables

The only thing you have to remember here is that you don’t mix different variables. You don’t know what $a$ and $b$ are (the variables are substituted for an unknown number, so you don’t know which numbers the variables represent). You don’t know if $a=b$, or if $a\ne b$. Therefore, $a+b$ is just $a+b$.

Example 1

Calculate and simplify

 $3a+2b-5a+8a-b$

Here, there are two different variables, $a$ and $b$. You have to calculate terms with $a$ and $b$ separately. Then you get

 $3a-5a+8a+2b-b=6a+b$