How do you solve 9=7z-13z-21?

2 Answers
Apr 15, 2018

z=-5

Explanation:

You combine 7z and -13z to get -6z, so

9=-6z-21

Add 21 to both sides

30=-6z

Divide both sides by -6

-5=z

Apr 15, 2018

z = -5

Explanation:

When solving equations, we can combine like terms as shown below:

5x + 4x -> 9x

So to solve this problem, we need to isolate the variable "z"
We do this by combining all terms with the variable z on them.

9 = 7z - 13z - 21

9 = -6z - 21

Then we treat it as a regular algebra problem by isolating the variable

9 = -6z - 21

30 = -6z

z = -5

Note: Combining like terms can only be done with variables of the same degree, or in other words, variables raised to the same exponent. Example below:

5z + 3z^2 cannot be combined into one expression, but

3z^2 + 5z^2 can be combined to produce 8z^2