How do I rearrange an equation involving multiple variables and fractions?

  • Context: High School 
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Discussion Overview

The discussion revolves around the process of rearranging an equation involving multiple variables and fractions, specifically focusing on making one variable the subject of the equation. Participants explore different methods of manipulation and notation in the context of algebraic expressions.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant describes their struggle with rearranging the equation a = bcde to isolate c, expressing confusion about the correct notation for divisions and fractions.
  • Another participant suggests that instead of dividing sequentially by b and d, one can divide by the product bd, leading to the expression cde/d = a/(bd).
  • It is noted that the notation (a/b)/d is equivalent to a/(bd), and participants discuss how to properly format these expressions in a way that avoids misinterpretation in a computer test.
  • Concerns are raised about the potential for misinterpretation of the notation a/bxd, which could be read differently than intended, emphasizing the importance of clarity in mathematical writing.

Areas of Agreement / Disagreement

Participants express differing views on the best approach to rearranging the equation and the correct notation to use, indicating that there is no consensus on a single method or format.

Contextual Notes

Participants assume that none of the variables b, d, and e are zero, which is crucial for the validity of their manipulations. There is also an emphasis on the importance of notation in the context of a computer test, which may affect how expressions are interpreted.

treacleybeak
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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 I am 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 can't get my head round it and google brought me to you guys

help...
 
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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:
\frac{\frac{a}{b}}{d} = \frac{a}{b d}

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.
 
\frac{\frac{a}{b}}{d} = \frac{a}{b d}


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 that's the problem as its on a computer test and if i put a space or symbol in the wrong place i don't get another chance
 
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.
\frac{a}{b} \times d

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

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