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Math Help - [SOLVED] f(b)<f(a)

  1. #1
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    [SOLVED] f(b)<f(a)

    Barron SAT Math II page 15 #21.

    If a and b are the domain of a function and f(b)<f(a), which of the following must be true?

    a) b<a

    b) b<a (error)

    c) a=b

    d)a ≠ b

    e) a=0 or b=0.

    The answer is d). Why? Why isn't it a)?

    Thanks in advance
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  2. #2
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    We rule out a because it is not always the case. You don't know if the function is increasing or decreasing.

    We rule out c because if it was true, the function in question wouldn't be a function.

    We're also not sure about e as well. It is possible, but we don't know for sure.

    But the one you are 100% sure of is that d) they are not equal. If they were equal, then we have a contradiction.
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