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anonymous

  • one year ago

Can someone set up this question for me? I am really struggling/: 5x - 2y + 3z = -23 -x - 2y + 2z = 5 10x + y - 4z = -11 Q1 choose a fav variable A1 Q2 pick a pair of equations, eliminate the fav variable A2 Q3 pick another pair, eliminate that same fav A3 Q4 now you have only 2 variables in 2 equations, like a+b=7 & a-2b=13 A4 Q5 pick a second fav A5 Q6 add equations together and eliminate it A6 Q7 solve for second fav A7 Q8 sub second fav into equation and find last variable A8

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  1. phi
    • one year ago
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    How about starting with y and the first two equations 5x - 2y + 3z = -23 -x - 2y + 2z = 5 subtract the bottom equation from the top equation can you do that ?

  2. anonymous
    • one year ago
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    @phi 4x + 5z = -28 ??

  3. phi
    • one year ago
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    the easiest (or at least likely to make mistakes) is to first multiply the 2nd equation by -1 that means multiply both sides and all terms by -1 -1*(-x - 2y + 2z ) = -1*5 distribute the -1. we get \[-1\cdot -x + -1\cdot-2y + -1\cdot2z = -5\\ x+2y -2z = -5 \] now we add, term by term the top equation and this new equation 5x - 2y + 3z = -23 x+ 2y - 2z = -5 what do you get ?

  4. phi
    • one year ago
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    can you add 5x+x ?

  5. anonymous
    • one year ago
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    @phi 6x

  6. anonymous
    • one year ago
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    @phi 6x + z = -28 now what?

  7. anonymous
    • one year ago
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    @triciaal

  8. anonymous
    • one year ago
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    I dont know what to do now for Q5-Q8 ?? :(

  9. phi
    • one year ago
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    ok that looks good. now pick the 2nd and 3rd equations -x - 2y + 2z = 5 10x + y - 4z = -11 and we again want to "get rid of y" multiply the second equation in that pair by 2 (all terms) can you do that ?

  10. anonymous
    • one year ago
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    multiply just 10x + y - 4z = -11 by 2 ?

  11. anonymous
    • one year ago
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    what do i do with the other? @phi

  12. triciaal
    • one year ago
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    You will add it to the new equation you get when you do the multiplication

  13. triciaal
    • one year ago
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    so go ahead and do the multiplication and show what you get

  14. anonymous
    • one year ago
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    20x + 2y + 8z = -22

  15. triciaal
    • one year ago
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    sure he will be back he is going through all the steps with you

  16. anonymous
    • one year ago
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    thank you @triciaal is that equation correct?

  17. triciaal
    • one year ago
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    not exactly watch your signs

  18. anonymous
    • one year ago
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    -8z ?

  19. triciaal
    • one year ago
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    yes

  20. anonymous
    • one year ago
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    so now that i have done that, what do i put into this? Q5 pick a second fav A5 Q6 add equations together and eliminate it A6 Q7 solve for second fav A7 Q8 sub second fav into equation and find last variable A8

  21. anonymous
    • one year ago
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    like how do i explain and set that all up into these questions?

  22. anonymous
    • one year ago
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    because I have this so far.. does it look correct? 5x - 2y + 3z = -23 -x - 2y + 2z = 5 10x + y - 4z = -11 Q1 choose a fav variable A1 y Q2 pick a pair of equations, eliminate the fav variable A2 5x - 2y + 3z = -23 - -x - 2y + 2z = 5 = 4x + 5z = -28 Q3 pick another pair, eliminate that same fav A3 6x + z = -28 Q4 now you have only 2 variables in 2 equations, like a+b=7 & a-2b=13 A4 4x + 5z = -28 & 6x + z = -28

  23. phi
    • one year ago
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    we are doing Q2 we picked the 2nd and 3rd equations -x - 2y + 2z = 5 10x + y - 4z = -11 . You multiplied the 2nd of that pair by 2. you now have the equations -x - 2y + 2z = 5 20x + 2y - 8z = -22 now add those two equations. what do you get?

  24. phi
    • one year ago
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    oops , we are doing Q3 Q2 is what we got from the first two equations, up above.

  25. anonymous
    • one year ago
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    so Q3 is 6x + z = -28 ??

  26. phi
    • one year ago
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    FYI the answer for Q2 Here are the steps 5x - 2y + 3z = -23 -x - 2y + 2z = 5 <-- multiply by -1 and add to the top equation. we get 6x + z = -28

  27. anonymous
    • one year ago
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    yeah! that is what I did..

  28. phi
    • one year ago
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    for Q3 we picked the 2nd and 3rd equations -x - 2y + 2z = 5 10x + y - 4z = -11 . You multiplied the 2nd of that pair by 2. you now have the equations -x - 2y + 2z = 5 20x + 2y - 8z = -22 now add those two equations. what do you get?

  29. anonymous
    • one year ago
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    i got 19x - 6z = -17

  30. phi
    • one year ago
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    ok, that is the last part of the answer for Q3

  31. anonymous
    • one year ago
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    Q1 choose a fav variable A1 y Q2 pick a pair of equations, eliminate the fav variable A2 5x - 2y + 3z = -23 - -x - 2y + 2z = 5 = 4x + 5z = -28 Q3 pick another pair, eliminate that same fav A3 -x - 2y + 2z = 5 + 20x + 2y - 8z = -22 = 19x - 6z = -17

  32. phi
    • one year ago
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    for Q4 we have these equations 6x + z = -28 19x - 6z = -17 for Q5, pick z as the "favorite variable"

  33. anonymous
    • one year ago
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    did i put it in those answers correctly so far?

  34. phi
    • one year ago
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    looks good.

  35. phi
    • one year ago
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    for Q6 6x + z = -28 <--- multiply all terms by 6 19x - 6z = -17

  36. anonymous
    • one year ago
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    Q4 now you have only 2 variables in 2 equations, like a+b=7 & a-2b=13 A4 6x + z = -28 & 19x - 6z = -17 Q5 pick a second fav A5 z Q6 add equations together and eliminate it A6 6x + z = -28 + 19x - 6z = -17 = 25x - 5z = -45

  37. anonymous
    • one year ago
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    it said add equations together ?

  38. phi
    • one year ago
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    unless there is a typo in the original equations, we can't just add them first we multiply the first one by 6 (this will give us a 6z term that will cancel the -6z in the other equation)

  39. anonymous
    • one year ago
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    36x + 6z = -168

  40. anonymous
    • one year ago
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    multiplied by 6 ^

  41. phi
    • one year ago
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    now we can add the equations

  42. anonymous
    • one year ago
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    ok..which equations?

  43. phi
    • one year ago
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    19x - 6z = -17 36x + 6z = -168

  44. anonymous
    • one year ago
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    Q5 pick a second fav A5 z Q6 add equations together and eliminate it A6 36x + 6z = -168 + 19x - 6z = -17 Q7 solve for second fav A7 55x = 185

  45. anonymous
    • one year ago
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    is this correct? @phi

  46. phi
    • one year ago
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    except -168 + -17 is not 185

  47. anonymous
    • one year ago
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    -185 ?

  48. anonymous
    • one year ago
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    now what about for Q8 ?

  49. phi
    • one year ago
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    yes, so 55x= -185 divide both sides by 55 \[ x = - \frac{185}{55}= - \frac{37}{11} \]

  50. anonymous
    • one year ago
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    5x - 2y + 3z = -23 -x - 2y + 2z = 5 10x + y - 4z = -11 Q1 choose a fav variable A1 y Q2 pick a pair of equations, eliminate the fav variable A2 5x - 2y + 3z = -23 - -x - 2y + 2z = 5 = 4x + 5z = -28 Q3 pick another pair, eliminate that same fav A3 -x - 2y + 2z = 5 + 20x + 2y - 8z = -22 = 19x - 6z = -17 Q4 now you have only 2 variables in 2 equations, like a+b=7 & a-2b=13 A4 6x + z = -28 & 19x - 6z = -17 Q5 pick a second fav A5 z Q6 add equations together and eliminate it A6 36x + 6z = -168 + 19x - 6z = -17 x= -37/11 Q7 solve for second fav A7 55x = -185 Q8 sub second fav into equation and find last variable A8

  51. anonymous
    • one year ago
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    like that? @phi

  52. phi
    • one year ago
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    yes, but when you show the equations, you should put them on separate lines something like this: A6 36x + 6z = -168 + 19x - 6z = -17 ------------------- 55x = -185 x = -185/55 = -37/11

  53. phi
    • one year ago
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    for A7, use 19x - 6z = -17 replace x with -37/11

  54. anonymous
    • one year ago
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    lol i am confused now ... can u copy and paste that Q&A format in the beginning so i can see?

  55. phi
    • one year ago
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    you wrote Q6 add equations together and eliminate it A6 36x + 6z = -168 + 19x - 6z = -17 x= -37/11 it would be clearer if you wrote it as A6 36x + 6z = -168 + 19x - 6z = -17 ------------------- 55x = -185 x = -185/55 = -37/11

  56. anonymous
    • one year ago
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    oh ok

  57. anonymous
    • one year ago
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    what about Q8 ?

  58. phi
    • one year ago
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    for A7, use 19x - 6z = -17 replace x with -37/11

  59. phi
    • one year ago
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    are you stuck?

  60. anonymous
    • one year ago
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    yes! @phi

  61. anonymous
    • one year ago
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    just for Q8 idk what to put

  62. phi
    • one year ago
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    first we have to do Q7 Q7 solve for second fav

  63. phi
    • one year ago
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    to do that we start with one of the equations from A4 for example, we can use 6x + z = -28 x is -37/11 replace x with that number. we want to find what z is

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