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Thread: Seemingly incorrect order of operations in this problem?

  1. #1
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    Question Seemingly incorrect order of operations in this problem?

    In my Algebra lessons, I've run into this problem: 2√(x−5)+7=13.

    The first thing that I did was divide the left and right side by 2. That's how the order of operations works, right? Multiplication before subtraction.
    However, when I saw the answer, the first thing done was subtracting both sides by 7. How does that work?
    Last edited by IgnisAckerman; Jun 7th 2017 at 06:20 PM.
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  2. #2
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    Re: Seemingly incorrect order of operations in this problem?

    If you multiply then add, to "undo" that, you need to undo in reverse order. Subtract then divide. Let's try with easier numbers: 2*3+4=10. By order of operations, we multiply first 2*3, then add 4. To undo that, we subtract 4 from both sides: 2*3+4-4=10-4
    2*3=6

    Then divide both sides by 2:
    3=3 is true.
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