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Math Help - rearranging fomulae help

  1. #1
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    Post rearranging fomulae help

    dont have a clue how to do this. can someone show me as well as the steps if u have the time with the answer.
    these are some questions we got during class(make x the subject).. sry dont know to get squared and cubed signs on here.

    sry pretty long post

    1. y= ax+ bx

    2. y= 3x/m +2x


    3. y=mx(squared)-a/b


    4. y= 1/3 mx(cubed)


    5. y= x/y + y/2


    6. y= 1/2 mx+ kx


    7. m(x-y)=3 (2x-7)


    8. y=mx-abx/3


    9. y= 4/x + c


    10. y= x+a/x+b
    Last edited by maths noob; October 1st 2009 at 11:16 AM.
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  2. #2
    Member SENTINEL4's Avatar
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    Quote Originally Posted by maths noob View Post

    1. y= ax+ bx
    y=ax+bx \Rightarrow y=(a+b)x \Rightarrow x=\frac{y}{a+b}

    You want something like this to do?
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  3. #3
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    yes
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  4. #4
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by maths noob View Post
    3. y=mx(squared)-a/b
    y = mx^2 - \frac{a}{b}

    (I assume m, a and b are all constants)

    Add \frac{a}{b} to both sides:

    y + \frac{a}{b} = mx^2

    Divide both sides by m:

    \frac{y}{m}+\frac{a}{bm}

    Take the square root of both sides - not forgetting the \pm sign:

    x = \pm \sqrt{\frac{y}{m}+\frac{a}{bm}}

    Can you try one now?
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  5. #5
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    i actually just got help off someone so i can do 1,2,3,5 type questions now

    would no.9 be

    y=4/x=c

    y= 4+cx

    y+4/c=x???

    anyways could you post how to do and answers to 4,6-10 just so i can get a better feel then having a go afterwards
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  6. #6
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by maths noob View Post
    4. y= 1/3 mx(cubed)


    6. y= 1/2 mx+ kx


    7. m(x-y)=3 (2x-7)


    8. y=mx-abx/3


    9. y= 4/x + c


    10. y= x+a/x+b


    anyways could you post how to do and answers to 4,6-10 just so i can get a better feel then having a go afterwards
    I'll post the answers because I don't want my working copied verbatim

    4. \sqrt[3]{\frac{3y}{m}}

    6. x = \frac{y}{0.5m+k} = \frac{2y}{m+2k}

    7. x = \frac{my-21}{m-6} = \frac{21-my}{6-m}

    8. x = \frac{3x}{3m-ab} = \frac{x}{m-\frac{1}{3}ab}

    9. x = \frac{4}{y-c}

    10. x = \frac{a-yb}{y-1}
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  7. #7
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    but how am i meant to know how to do them to get to the answer?
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  8. #8
    Super Member Matt Westwood's Avatar
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    Quote Originally Posted by maths noob View Post
    i actually just got help off someone so i can do 1,2,3,5 type questions now

    would no.9 be

    y=4/x=c

    y= 4+cx

    y+4/c=x???

    anyways could you post how to do and answers to 4,6-10 just so i can get a better feel then having a go afterwards
    Nope.

    y = 4/x + c

    Multiply it all by x:

    xy = 4 + cx

    Gather all the x's on one side:

    xy - cx = 4

    Get x in one place:

    x (y-c) = 4 (this is an example of use of the distributive law)

    x = \frac 4 {y-c}
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  9. #9
    Super Member Matt Westwood's Avatar
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    Quote Originally Posted by maths noob View Post
    but how am i meant to know how to do them to get to the answer?
    Same way as you learn to do anything. Watch what's being done, imitate it, then apply the technique.
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