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Math Help - Proofs using real numbers and integers

  1. #1
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    Proofs using real numbers and integers

    Hello, didn't know exactly where to post this. Any guidance would be much appreciated. Thanks.

    Let a,b, and c be integers and x,y and z be real numbers. Use the technique of working backward from the desired conclusion to prove that

    a). [(x+y)/2] ≥(greater than or equal to) (sqrt)√(x*y)

    b.) If x^3 + 2*x^2 < 0 , then 2*x + 5 < 11

    c). If an isoceles triangle has sides of length x,y and z, where x=y and z=(sqrt)√(2*x*y), then it is right triangle
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  2. #2
    Super Member TheChaz's Avatar
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    Re: Proofs using real numbers and integers

    "working backwards..." - ???
    Is that like the converse?

    If x^3 + 2x^2 = x^2(x + 2) < 0, then x + 2 < 0 ... i.e. x < -2

    Not sure how that relates to 2x + 5 < 11
    <=>
    x < 3
    ???
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  3. #3
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    Re: Proofs using real numbers and integers

    i think it means if 2*x + 5 < 11 then prove x^3 + 2*x^2 < 0
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