MATH

5x-4y= -3
2x + 7y= 5
How to solve this linear system shown above by using elimination strategy ?


(5x-4y= -3) *2 ->10x - 12y= 6
(2x + 7y= 5) *5 -> 10 +35y= 25
___________________________________________
-47y = -19
y = -19/47

10x - 12y= 6
10x - 12(0.4) = 6
10x -4.8=6
x=1.08

I seem to get the final answer wrong. correct me if Im wrong overtime i verify. THanks

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asked by td
  1. You're doing the elimination method right. :) But there's just some errors in multiplying. In your first equation (5x - 4y = -3), you multiplied it by 2.
    5x * 2 = 10x, yes that's right.
    -4y * 2 = -8y, not -12y as you've typed.
    -3 * 2 = -6, not 6 as you've typed.

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    posted by Jai
  2. oh sorry, I know I type it in wrong number. But even I tries in correct number. I still didn't get it right?

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    posted by td
  3. Why is that? Anyway, let's solve for y. I'll multiply the first equation by -2 instead of 2:

    (5x - 4y = -3) * -2 ---> -10x + 8y = 6
    (2x + 7y = 5) * 5 ---> 10x + 35y = 25

    Add them together:
    -10x + 8y = 6
    10x + 35y = 25
    ----------------------
    43y = 31
    y = 31/43

    Now that you have a value for y, substitute this to either equation to get x. Let just choose the first equation:
    5x - 4y = -3
    5x - 4(31/43) = -3
    x = ?

    hope this helps~ `u`

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    posted by Jai

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