Confused about what the book say's!!!!!

[redranger7018]

Hello, been in this pre-algebra class for a wile and I’m having the most difficult time with the book. In all the examples are written horizontally which is confusing, because the steps are not broken down, just a series of numbers and a few signs and no explanations as to how other numbers are coming up. My instructor has been showing me a way of doing thing in vertical columns, but I’m having trouble getting the right answers. Here is an example of one problem:

Solve:

3x - 7 = 4x + 5, the book say’s that the answer is -12, but I’m getting something else

3x / 3 = x,
7 / 3 = 2

4x / 4 = x,
5 * 4 = 20

I don’t know what else I’m to do to get -12

2 / 10 = 0, and

10 / 2 = 5

2 * 10 = 20, and

10 * 2 = 20

Where is the -12?

 

[redranger7018]

I'm sorry I forgot to put in this other information on what x is equal to in the equations, sorry.


Solve:

3x - 7 = 4x + 5, the book say’s that the answer is -12, but I’m getting something else

3x / 3 = x,
7 / 3 = 2
x = 2

4x / 4 = x,
5 * 4 = 20
x = 20

 

[Denis]

You need to have a talk with your teacher...

 

[letsgetaway]

I don't know if you still need the help, but I'll still post it.

-12 is the correct answer.

3x-7=4x+5
You must get x to one side of the equation. Let's put it on the left. Subtract -4x from both sides.
3x-7-4x=4x-4x+5
Simplify.
3x-4x-7=5
Now let's get all the numbers without the x-variable to the right side of the equation. So add 7 to both sides.
3x-4x-7+7=5+7
Simplify again.
-x=12
"X" cannot be negative. Multiply both sides of the equation by -1. This will make "X" positive and "12" negative.
(-1)-x=12(-1)

x = -12

And that's why the answer is -12.
Through some of the steps I assume you know the rules about signs. If not, look it up. It would be too much to type.

 

[redranger7018]

Hi letsgetaway, well I guess I've on to other stuff like add subtraction and multiplyiing, but this also helps. Thanks redranger7018@iowatelecom.net