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anonymous

  • one year ago

what is the solution of x+y=7 2x-4y=8

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  1. jim_thompson5910
    • one year ago
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    we have a `y` in the first equation and a `-4y` in the second equation adding them up gives: `y+(-4y) = -3y` which isn't 0 like we want however we can change that `y` to `+4y` by multiplying by 4. Then notice how `4y + (-4y) = 0y = 0`

  2. anonymous
    • one year ago
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    so it's 0?

  3. jim_thompson5910
    • one year ago
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    to change the y to 4y, we have to multiply both sides of the first equation by 4 x+y=7 4*(x+y)=4*7 4x+4y = 28

  4. jim_thompson5910
    • one year ago
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    This system x+y=7 2x-4y=8 turns into 4x+4y=28 2x-4y=8

  5. jim_thompson5910
    • one year ago
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    Do you see how to solve 4x+4y=28 2x-4y=8 ??

  6. anonymous
    • one year ago
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    i don't

  7. anonymous
    • one year ago
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    would you subtract?

  8. jim_thompson5910
    • one year ago
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    you add actually

  9. jim_thompson5910
    • one year ago
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    add straight down 4x+4y=28 2x-4y=8 ----------- 6x+0y = 36 so 6x = 36 which means x = ???

  10. anonymous
    • one year ago
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    6

  11. jim_thompson5910
    • one year ago
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    yes

  12. jim_thompson5910
    • one year ago
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    now take that x value and plug it into any equation that has x and y in it

  13. jim_thompson5910
    • one year ago
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    then solve for y

  14. anonymous
    • one year ago
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    12-47=8? am i doing that right?

  15. anonymous
    • one year ago
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    i mean 12-4y=8

  16. jim_thompson5910
    • one year ago
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    yes now solve for y

  17. anonymous
    • one year ago
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    is y 0?

  18. jim_thompson5910
    • one year ago
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    no

  19. jim_thompson5910
    • one year ago
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    try again

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