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Math Help - Justification for removing negatives on this algebra symbol manipulation question:

  1. #1
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    Justification for removing negatives on this algebra symbol manipulation question:

    Hi folks! Certainly glad this forum exists

    I'm following on how to do this till the very last step where -x1 is on the left and -x2 is on the right. I don't understand why one can simply remove both negatives or why they would negate each other on opposite sides of the equation?

    Here's the the question and solution:

    x1 & y1 and x2 & y2 are two points on a non-vertical line. X1 does not equal x2. The slope (M) of the line is:

    solve for x1
    Multiply on both sides, and divide M on both sides to begin isolating x1.
    ,
    .
    Then, by subtracting from both sides of the equation, we get
    ,
    ,
    .

    The 2nd to last step, both x's are negative. The last step they're positive. I'm not understanding how they remove them.
    Is it because it is representing a line that crosses the negative side to the positive side?

    Many thanks for any help!
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  2. #2
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    Multiply both sides of the equation by -1.
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  3. #3
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    lol thanks,

    I didn't know we were allowed to do that on lines!

    I'm completely humbled. Thank you haha
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