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octoberchick1011 Group Title

Solve the system using an augmented matrix. Please show all your steps! Thanks! (: -x -3y = -17 2x -6y = -26

  • one year ago
  • one year ago

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  1. amistre64 Group Title
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    can you set up the matrix?

    • one year ago
  2. octoberchick1011 Group Title
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    Yes: -1 -3 | -17 2 -6 | 26

    • one year ago
  3. jim_thompson5910 Group Title
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    Your next step is to make the upper left corner equal to 1. How do we do this?

    • one year ago
  4. octoberchick1011 Group Title
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    Umm.. I'm not entirely sure - I'm not very good at these types of problems. I think we would multiply by -3 right...?

    • one year ago
  5. jim_thompson5910 Group Title
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    What do we multiply -1 by to get 1 ?

    • one year ago
  6. jim_thompson5910 Group Title
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    -1 times ??? = 1

    • one year ago
  7. octoberchick1011 Group Title
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    -1.

    • one year ago
  8. jim_thompson5910 Group Title
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    so do this across the entire first row....ie multiply EVERY number in row 1 by -1

    • one year ago
  9. jim_thompson5910 Group Title
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    -1 -3 | -17 2 -6 | 26 1 3 | 17 -1*R1 2 -6 | 26

    • one year ago
  10. jim_thompson5910 Group Title
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    The notation -1*R1 means "-1 times Row 1"

    • one year ago
  11. octoberchick1011 Group Title
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    Okay so it would be: 1 3 | 17 right?

    • one year ago
  12. jim_thompson5910 Group Title
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    yes it would be

    • one year ago
  13. jim_thompson5910 Group Title
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    The upper left corner is a 1. This is known as the pivot (for the first column). Everything thing else must be a zero in order to obtain the solutions for x and y. So how to we turn that 2 (below the pivot of 1) into a 0 ?

    • one year ago
  14. jim_thompson5910 Group Title
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    oh sry, i made a typo the second row should be 2 -6 | -26 instead of 2 -6 | 26

    • one year ago
  15. octoberchick1011 Group Title
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    You would make the 2 a zero my by multiplying it by 0..? I think..

    • one year ago
  16. jim_thompson5910 Group Title
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    well if you did that, everything in row 2 would become 0

    • one year ago
  17. jim_thompson5910 Group Title
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    then you'd get 0x + 0y = 0...which is completely useless now

    • one year ago
  18. octoberchick1011 Group Title
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    Oh. That's true..

    • one year ago
  19. jim_thompson5910 Group Title
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    Instead, you can add/subtract multiples of row 1 to row 2

    • one year ago
  20. octoberchick1011 Group Title
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    So does that mean we would subtract 2 from row 2?

    • one year ago
  21. jim_thompson5910 Group Title
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    Notice in the first column we have 1 2

    • one year ago
  22. jim_thompson5910 Group Title
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    If we subtract row 1 from row 2, we get 2 - 1 = 1 But that's not zero However, if we subtract row 1 (twice) from row 2, we get 2 - 1 - 1 = 0

    • one year ago
  23. octoberchick1011 Group Title
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    Okay. So does that mean that row 2 looks like this now: 0 -6 | -26

    • one year ago
  24. jim_thompson5910 Group Title
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    not quite

    • one year ago
  25. jim_thompson5910 Group Title
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    -6 - 2*(-3) = -12 so the 2nd element in row 2 is -12

    • one year ago
  26. octoberchick1011 Group Title
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    Ugh, I'm so confused - lol, these kinds of probles frustrate me! :P

    • one year ago
  27. jim_thompson5910 Group Title
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    -26 - 2*17 = -60

    • one year ago
  28. jim_thompson5910 Group Title
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    so the 3rd element in row 2 is -60

    • one year ago
  29. jim_thompson5910 Group Title
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    after this, you should have 1 3 | 17 0 -12 | -60

    • one year ago
  30. jim_thompson5910 Group Title
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    what's next?

    • one year ago
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