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Sophia.13 Group Title

Part 1 (3 points) : When solving systems of equations, how do you determine what method to use? Part 2 (10 points) : Choose 1 system of equations from the choices below. Then, solve the system and post your solution, showing your steps so that other students can see which method you chose. –y + 3x = 6 y = –6x + 12 6x – 4y = 54 –9x + 2y = –69 2y = x + 1 –2x – y = 7

  • one year ago
  • one year ago

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  1. srossd Group Title
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    For part 1, it's basically whatever looks like it will be easiest. If you have a -5x in one equation and a 5x in the other, it's probably easiest to add them together. If you can easily solve for x or y, then substitution is probably easiest. But it doesn't matter if you don't make the best choice here, because each method will give you the correct answer.

    • one year ago
  2. srossd Group Title
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    For part 2, I'll work through the first one, and then you can try one of the others to make sure you understand. Here, we have that case I mentioned - a y in one of them, and a -y in the other. So I'll add them together, and get \[3x=-6x+18\] \[9x=18\] So x=2. Plug that back in to either equation, and you'll see that y=0.

    • one year ago
  3. Sophia.13 Group Title
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    So for part two, if i chose elimination what would i have to do?

    • one year ago
  4. srossd Group Title
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    This is embarrassing, but I don't know the names of all these methods, I just do em. What's elimination exactly?

    • one year ago
  5. srossd Group Title
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    If I remember correctly, it's just adding equations together like I did.

    • one year ago
  6. Sophia.13 Group Title
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    yes

    • one year ago
  7. Sophia.13 Group Title
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    2y = x + 1 –2x – y = 7 For this equation^

    • one year ago
  8. abb0t Group Title
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    matrices

    • one year ago
  9. srossd Group Title
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    You could use matrices, but that's overcomplicating things here.

    • one year ago
  10. srossd Group Title
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    When you don't have a nice matchup like 2x and -2x, you'll have to multiply one of them by something first. So for this example, multiply the top (or the bottom, but I'm choosing the top arbitrarily) by 2 and then add: 4y = 2x+2 -2x-y=7 4y+7=2-y 5y=-5 y=-1 Then plug that back in, and you'll get x=-3.

    • one year ago
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