# Need Equation/graphing help

1. Sep 20, 2004

### skyie1

I know next to nothing about this stuff, and have a problem that is due Monday... I have signed up with a tutor, but not able to begin studies until Thursday....
Anyway, my problem is as follows:
y=3x-4
5x+y=3

We are to solve for x and y using addition, subtraction and subsitution, and then graphicly, min of three points....

I would be thankful for any help......... Skyie

2. Sep 20, 2004

### arildno

Welcome to PF!
"x" and "y" are some two numbers, right?
(You don't know at the moment their values)
So, the first equation says:
y=3x-4
This means, that whatever values "x" and "y" have we have been told that "y" is equally big as 3 times x minus 4 (right?)
So, whenever we meet "y" (for example in your second equation), we might substitute 3x-4 for "y" (that expression has, by our first equation, the same value as "y")

3. Sep 20, 2004

### sdmcam

Hello I am hoping someone can help. My daughter has an equation she does not understand and I am unable to help her.

-5/8 x 16/21 x (-7/15)

I cannot seem to figure out what the common denominator would be for her to be able to work her way through this

Can anyone help????

4. Sep 20, 2004

### arildno

Hi, sdmcam :welcome to PF!

Now, as far as I can tell, you've gor an expression here which you want to simplify?
Is the "x" a multiplication sign?

5. Sep 20, 2004

### HallsofIvy

Staff Emeritus
First, this is not an equation, it is an "expression" (it's not an equation because it's not equal to anything).

Secondly, multiplying fractions, you don't need to find a "common denominator"- that's used in adding or subtracting fractions.

$$\frac{-5}{8}\frac{16}{21}\frac{-7}{15}$$

Notice that one fraction has 8 in the denominator and another has 16 in the numerator: 16/8= 2. One fraction has 5 in the numerator and the other has 15 in the denominator: 5/15= 1/3. One fraction has 21 in the denominator and another has 7 in the numerator: 7/21= 1/3. Finally, (-)(-)= +.

This is the same as
$$\frac{2}{(3)(3)}= \frac{2}{9}$$.