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Help rearranging an equation

  1. Apr 17, 2009 #1
    i have to rearrange and equation

    without using the exact terms its along the lines of a = bcde and i have to make c the subject. have searched my study materiel and im fine with multiplications etc and doing the same to both sides when doing the rearrangement ie
    bcde = a
    bcde divided by b = a cancel the b to get cde = a over b (as in a fraction) but how do i write the next divisions ie
    cde/d = a over b cancel d to get ce = a over b but where do i put d? do i put a at the top and b and d below with a space between or do i have to write ce = a/b/d

    just cant get my head round it and google brought me to you guys

    help.........
     
  2. jcsd
  3. Apr 18, 2009 #2

    CompuChip

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    I will assume that none of b, d and e are zero, otherwise dividing by any of them would be a problem anyway.

    If you go back to
    bcde = a​
    instead of first dividing by b and then by d, you can of course divide by bd. That gives you
    bcde/(bd) = cde/d = bce/b = be = a/(bd).​
    On the other hand, as you had reasoned already, you can first divide by b and then by d, giving be = (a/b)/d.
    This shows that (a/b)/d = a / (b d).
    Writing it in fractions: you can put whatever you divide by below the bar:
    [tex]\frac{\frac{a}{b}}{d} = \frac{a}{b d}[/tex]

    Also note that (a / b) / d is something else than a / (b / d). When in doubt, you can plug in some numbers. Say a = 12, b = 6, d = 3. Then (a / b) / d = (12 / 6) / 3 = 2 / 3 while a / (b / d) = 12 / (6 / 3) = 12 / 2 = 6.
     
  4. Apr 19, 2009 #3
    [tex]\frac{\frac{a}{b}}{d} = \frac{a}{b d}[/tex]


    but does this not indicate a/bxd?

    i struggled with fractions 22 years ago at school and never thought id need to bother with them again and while i get what to do with everything else its how to write the equation correctly thats the problem as its on a computer test and if i put a space or symbol in the wrong place i dont get another chance
     
  5. Apr 19, 2009 #4

    CompuChip

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    bd means b multiplied by d. It's also written as b d or b*d.
    Note that, when you type a/bxd into a computer, it will usually interpret it as (a/b)xd, i.e.
    [tex]\frac{a}{b} \times d[/tex]

    If you mean
    [tex]\frac{a}{b \times d}[/tex]
    you should write a/(bxd)
     
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