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student1988

Solve the inequality in terms of intervals. Interval notation (x + 4)(x − 3)(x + 8) ≥ 0

  • one year ago
  • one year ago

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  1. satellite73
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    zeros are at \(-8,-4,3\) so divide the real line up in to four intervals \[(-\infty, -8),(-8,-4),(-4,3),(3,\infty)\] it is clearly positive on the last intervals, so it will be negative, positive, negative, positive in that order

    • one year ago
  2. satellite73
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    since you want to know where it is positive, pick the second and fourth interval. because it is \(\geq\) and not \(>\) use closed brackets to write the interval

    • one year ago
  3. student1988
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    I'm a little confused. What are the interval that satisfy the equation?

    • one year ago
  4. satellite73
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    the second and fourth one you can check by plugging in a number in either of those intervals, and see that it is positive

    • one year ago
  5. student1988
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    (-8,-4)U(3,infinity) ?

    • one year ago
  6. student1988
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    How did you come to this answer?

    • one year ago
  7. satellite73
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    well you need square brackets, not round ones

    • one year ago
  8. satellite73
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    \(>0\) is a synonym for "positive" if \(x>3\) then all the factors are positive, so their product is positive as well since it changes sign at the zeros, you know it is "negative" then "positive" then "negative" then "positive"

    • one year ago
  9. satellite73
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    you could also check by noting that if \(x<-8\) all the factors are negative since the product of three negative numbers is also negative, you know on \((-\infty,-8)\) the whole thing is negative

    • one year ago
  10. satellite73
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    but don't forget to use square brackets, not round ones

    • one year ago
  11. student1988
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    ok, thank you very much for your help! I don't have a book at this moment that explained inequalities and factoring and I am reviewing. You've been a great help. Thanks! :)

    • one year ago
  12. satellite73
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    yw

    • one year ago
  13. davisla
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    These are 2 older videos I made with similar examples. Perhaps they would help. www.mathmods.com/mat115/chapters/chapt2/Quadratic_Inequalities1/Quadratic_Inequalities1.html www.mathmods.com/mat115/chapters/chapt2/Quadratic_Inequalities_2/Quadratic_Inequalities_2.html

    • one year ago
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