## lovelycharm 2 years ago elimination 4x - 7y = 3 x - 7y = -15

1. mjr632

Do you understand how to substitute?

2. lovelycharm

yeh

3. mjr632

Okay, firstly, you want one equation as either Y or X by itself.

4. mjr632

If you do that part, i'll then explain the next step.

5. lovelycharm

okay wat the next step

6. mjr632

write the equation you've got for your isolated variable in here.

7. lovelycharm

|dw:1360887641308:dw| is that right how i solve for y

8. Rachel98

- 7y + - 7y is not zero and 4x + x is 5x

9. Rachel98

You need a variable to cross out when you add down. Try multiplying one of the equations by a certain number so that one variable crosses out when you add down.

10. lovelycharm

could u show me the step please @Rachel98

11. Rachel98

Okay, here is an example problem I'll draw it.

12. Rachel98

|dw:1360888023089:dw|

13. Rachel98

Now see how none of the variables cross off? So I'm going to try multiplying the first equation by - 1 and see what happens.

14. Rachel98

|dw:1360888146491:dw|

15. Rachel98

Now see if you add straight down a variable crosses off when you add down. - y and y can also be put as - 1y and 1y. Look at the numbers - 1 + 1 = 0, so that crosses off.

16. Rachel98

|dw:1360888346035:dw|

17. Rachel98

Now all we have to do is divide both sides by - 1, so undo the multiplication

18. Rachel98

|dw:1360888489391:dw|

19. Rachel98

So we have our x value, now what about y? What we do is we plug in the x value (substitute 8 for x) in one of the original equations. In this case the bottom equation is easier to do this.

20. lovelycharm

could u help me with my problem cuz i dont understand ur problem

21. Rachel98

|dw:1360888601809:dw|

22. Rachel98

See, in my problem how I multiplied one equation by - 1? Try doing that with either one of your equations and then add down.

23. Rachel98

Remember, a negative * a negative is a positive.

24. Rachel98

|dw:1360888933281:dw|

25. Rachel98

Did you get it? Give it a try. I'll check your answer and if you make a mistake I'll work through it for you.