Algebra 1 question

1. Jun 28, 2005

staples82

If 3x+4y=7 and 2y=6x+6, then what is xy?

3X+4y=7
-6X+2y=6

(2)3X+4y=7 which goes to 6X+8Y=14

I cross the X out, subtract and get 6y=8

then I got 4/3
and final answer i got was 20/3

HOWEVER, the answer says is is -2/3 ... I don't understand how that is the answer...

2. Jun 28, 2005

dextercioby

Daniel.

3. Jun 28, 2005

staples82

i don't understand...

4. Jun 28, 2005

dextercioby

$$\left\{\begin{array}{c} 6x+8y=14 \\ -6x+2y=6 \end{array} \right$$

As i said before,add the two equations,so you'd eliminate "x".

Daniel.

5. Jun 28, 2005

staples82

yeah, then i got 6y=8

6. Jun 28, 2005

dextercioby

Daniel.

7. Jun 28, 2005

staples82

oh, my bad ....2, so do I plug it back in, sorry I am going into 7th grade, learning this from a book.

update: ok I understand what you said, now I have y=2...

Last edited: Jun 28, 2005
8. Jun 28, 2005

Jameson

Yes, you are correct that y=2. Now as you said plug it back in to find the unknown x.

$$3x + 4y = 7$$

You know what to do.

Jameson

9. Jun 28, 2005

staples82

thank you, dextercioby and Jameson, I understand the problem now.