## Thinking Mathematically (6th Edition)

The terms 13$x^{2}$ and 10x cannot be combined 23$x^{2}$ because 13$x^{2}$ and 10x are not like terms. Like terms must have the EXACT same variable parts. The two terms have different variable parts: one has the variable part $x^{2}$ and the other just has a plain x. There is nothing that can be done to combine the two terms (as written) using either addition or subtraction.