Combine like terms.

in 12.) , if your mean 7x^4 etc, then all 3 terms would be different and nothing else can be done

13.)
3-4x - 15x - 6x - 1
= 2 - 24x , just add up the x terms and the constants.

Thank you so much Reiny :D

To combine like terms, you need to add or subtract terms that have the same variable raised to the same power.

12.)
In the expression 7r^4 + 13r^2 + 9r, we have three terms. However, there are no other terms with the same variable raised to the same power. Therefore, we cannot combine any like terms in this case.

13.)
In the expression 3 - 4x - 15x - 6x - 1, we have several terms with the variable 'x'. To combine like terms, we need to group the terms with 'x' together.

First, let's reorder the terms:

3 - 4x - 15x - 6x - 1

Next, let's combine the terms with 'x':

-4x - 15x - 6x

We can simplify this by adding the coefficients of 'x':

-4x - 15x - 6x = -25x

Now, let's put it all together:

3 + (-25x) - 1

We can simplify further:

3 - 1 - 25x = 2 - 25x

So, the combined form of the expression is 2 - 25x.