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Math Help - Inequality Problem

  1. #1
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    Inequality Problem

    Hello, Could you help me with these two inequalities? , all of them taken of Precalculus Stewart Book, Chapter 1, Exercise 1.7.
    The first is:
    -2x^2 ≤ 4
    The answer must be (-∞, ∞)
    but I got as last result x^2 ≥ -2
    and it can't be root of 2, because it would be a complex number, can I?
    I can't either factorize or something else.
    The second is 2/5 x + 1< 1/5 -2x
    and this book only have solutions for odd numbers, this is number sixteen, I got:
    10/5 x + 1 < 1-2x
    x +1 < 1-2/2 x
    x < 1/2
    I did it wrong?
    Ah I forgot it... I have doubts of when change the sign 'greater than' for 'less than"
    Still confused about that.
    Thanks
    Last edited by stephanice; February 12th 2013 at 06:20 PM.
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  2. #2
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    Re: Inequality Problem

    Quote Originally Posted by stephanice View Post
    Hello, Could you help me with these two inequalities? , all of them taken of Precalculus Stewart Book, Chapter 1, Exercise 1.7.
    The first is:
    -2x^2 ≤ 4
    The answer must be (-∞, ∞)
    but I got as last result x^2 ≥ -2
    and it can't be root of 2, because it would be a complex number, can I?

    Why are you doing any work at all?
    STOP! Step back. Look at the problem.

    It is true for all x.
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