math

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We are learning inequalities and I just did some homework but the teacher returned it saying I did some of them wrong.
1. -2x - 10 < 2
2. -2x + 15 < 17
I didn't flip the inequality sign when I divided by (-2).
But why do we always have to flip the sign when we multiply or divide by a negative number?

  • math -

    In google type:
    inequalities and negative numbers

    You will find couple sites.
    mathforum is good.


    1.

    -2 x - 10 < 2

    -2 x < 2 + 10

    -2 x < 12 Divide both sides with -2

    x > 12 / - 2

    x > - 6


    2.

    -2x + 15 < 17

    -2 x < 17 - 15

    -2 x < 2 Divide both sides with -2

    x > 2 / -2

    x > -1

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