# How do you combine like terms for -7mn-2mn^2-2mn + 8?

##### 1 Answer
Dec 24, 2014

In this expression only the first $- 7 m n$ and the third $- 2 m n$ are like terms. They both have the same literary part $m n$ to the same powers and they can be added together.
The second term $- 2 m {n}^{2}$ has $m n$ as well BUT $n$ is raised to the power $2$!!!

Imagine that like terms are objects. You can add or subtract together the same objects (for example 5 apples+2 apples= 7 apples) while you CANNOT do it with different objects (for example: 3 apples + 5 chairs=???)

In your case you can now write:

$- 7 m n - 2 m {n}^{2} - 2 m n + 8$ as:
$\left(- 7 m n - 2 m n\right) - 2 m {n}^{2} + 8$
$- 9 m n - 2 m {n}^{2} + 8$