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Math Help - Function Notation help!

  1. #1
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    Function Notation help!

    Given f(x) = √x - 2, find: 3f(4(x-1)) + 5

    I cannot get started.
    Last edited by mr fantastic; August 30th 2009 at 08:48 PM. Reason: Removed excessive ! in post title
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  2. #2
    Super Member Matt Westwood's Avatar
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    Think of f as "doing something" to what's in the bracket.

    In this case f means "take the square root and subtract 2".

    So look at what you have:

    3f(4(x-1)) + 5

    In the brackets defining the f there's 4(x-1).

    So do the square root of all that and subtract 2. Then when you done that, multiply the whole thing by 3 and then add 5.
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  3. #3
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    kk ill try that and get back to you tomorrow
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  4. #4
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    i still cant get it man

    can u show me a step by step?

    this is how far i get

    Given f(x) = √x - 2, find: 3f(4(x-1)) + 5

    f(x) = √(4x-4)

    Basically I dumbed down the brackets of (4(x-1)) to (4x-4) and put that in for x, but I don't know what to do from there....
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  5. #5
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    mr fantastic's Avatar
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    Quote Originally Posted by quick.on.my.feet View Post
    i still cant get it man

    can u show me a step by step?

    this is how far i get

    Given f(x) = √x - 2, find: 3f(4(x-1)) + 5

    f(x) = √(4x-4)

    Basically I dumbed down the brackets of (4(x-1)) to (4x-4) and put that in for x, but I don't know what to do from there....
    f(4(x - 1)) = \sqrt{4(x - 1)} - 2.

    3 f(4(x - 1)) = 3 (\sqrt{4(x - 1)} - 2).

    3 f(4(x - 1)) + 5 = 3 (\sqrt{4(x - 1)} - 2) + 5.

    Simplify.
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  6. #6
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    that's exactly what i did, but idk how to dumb down the square root and stuff.
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  7. #7
    Super Member Matt Westwood's Avatar
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    One thing you can do is note that:
    \sqrt {4 (x-1)} = \sqrt 4 \sqrt {x-1} = 2 \sqrt {x-1}
    and then you can tidy up the rest without bothering to do anything else with what's under the square root.
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  8. #8
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    ok my teacher explained it to me
    I didn't know i had to multiply the WHOLE thing by 3
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