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Math Help - Help: f(x)=0

  1. #1
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    Question Help: f(x)=0

    Intro Calculus help

    f(x) = x^2+4x-5

    Find x such that f(x) = 0

    I know it would be:


    x^2+4x-5 = 0
    (x+5)(x-1)=0

    So,the answer would be x=-5 or x=1.
    But how would I explain that the signs (+ and -) would switch around, as I have to give full working out?

    Thanks in advance
    Last edited by starship; March 2nd 2008 at 01:29 AM.
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  2. #2
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    Quote Originally Posted by starship View Post
    Intro Calculus help

    f(x) = x^2+4x-5

    Find x such that f(x) = 0

    I know it would be:


    x^2+4x-5 = 0
    (x+5)(x-1)=0

    Mr F adds: Therefore either x + 5 = 0 or x - 1 = 0.

    So,the answer would be x=-5 or x=1.
    But how would I explain that the signs (+ and -) would switch around, as I have to give full working out?

    Thanks in advance
    ..
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  3. #3
    Bar0n janvdl's Avatar
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    Quote Originally Posted by starship View Post
    Intro Calculus help

    f(x) = x^2+4x-5

    Find x such that f(x) = 0

    I know it would be:


    x^2+4x-5 = 0
    (x+5)(x-1)=0

    So,the answer would be x=-5 or x=1.
    But how would I explain that the signs (+ and -) would switch around, as I have to give full working out?

    Thanks in advance
    Because each bracket should equal 0.

    So how would (x + 5) = 0 ?
    If x = -5 then the bracket equals zero.

    Same goes for the other bracket.

    ---

    Normally no-one expects you to explain this part anyway. So i wouldn't worry about it.
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