## EmmaH 2 years ago is -x-4x=3x??

1. JoãoVitorMC

only if x=0

2. mathstudent55

-x is the same as -1x -4x is -4 x If you had -1 -4 what do you get?

3. mathstudent55

-1 - 4 = ?

4. EmmaH

-5?

5. EmmaH

im having a lot of trouble with this Solve the system. y = 2 - x and y = 4x + 7 (1, 1) (1, 3) (-1, 3) (-1, 1) no solution im prettyy sure tis no solution

6. mathstudent55

Right, so since -1 - 4 = -5, then -x - 4x = -5x

7. mathstudent55

Now the system. Again, you have the two equations solved for y already, so use substitution.

8. mathstudent55

Do you remember from the two previous systems what to do next?

9. EmmaH

yes im working ion it

10. mathstudent55

Ok, let me see what you're up to since you're having trouble with it.

11. EmmaH

ok so i had 2-x=4x+7 2-x +2=4x+7+2 -x=4x+9 -x-4x=9 now im stuck

12. mathstudent55

The 2 on the left side is positive, so you need to subtract 2 from both sides.

13. seanwalsh1984

-x (so -1x) take away 4 more x's. It's like being \$1 in the hole in the bank account. Spend four more bucks, and you are \$5 in the whole, not \$3. However... -x - 4x = 3x is interesting because: -x - 4x + x = 3x + x Then we have -4x = 3x Then as said above, if x = 0, then it is true, otherwise no. Hope this helps.

14. mathstudent55

2 - x = 4x + 7 2 - 2 - x = 4x + 7 - 2 -x = 4x + 5 Now subtract 4x from both sides

15. EmmaH

-4-4x=5

16. mathstudent55

-x - 4x = 4x - 4x + 5 -5x = 5

17. EmmaH

x=-1?

18. mathstudent55

|dw:1356283149364:dw|

19. mathstudent55

right, x = -1

20. mathstudent55

Now insert this value of x in one of the original equations, and solve for y

21. EmmaH

sorry i had to do something i do it one sec

22. EmmaH

1,3 ?

23. mathstudent55

y = 3. You're right, but remember x = -1, not x = 1

24. EmmaH

thanks you!

25. mathstudent55

|dw:1356283635553:dw|

26. mathstudent55

You're welcome.

27. EmmaH

one more question The ordered pair (-1, -1) is a solution of the system -4x + 2y = 2 and x + y = -2. True False

28. EmmaH

i think its true

29. mathstudent55

Substitute the ordered pair into both equations. If it makes them both true, it's a solution.

30. EmmaH

ok i did it its true

31. mathstudent55

-4x + 2y = 2 Try (-1, -1) Is -4(-1) + 2(-1) = 2 ? 4 - 2 = 2? Yes. The ordered pair works in the first equation. Now try the second. x + y = -2 Is -1 + (-1 ) = -1 true? -2 = -2. It's true. You are correct, (-1, -1) is a solution.

32. mathstudent55

Good job!

33. EmmaH

=D