# Rearrange of formula

Tags: rearrange formulae
 P: 61 1. The problem statement, all variables and given/known data I am trying to rearrange formula to make r^2 the subject. 2. Relevant equations 0.05=(2.88/4*1*0.018)(0.05^2-r^2) 3. The attempt at a solution I tried to rearrage as : 0.05^2+0.05/2.88/4*0.018 then sqr root of the answer but I dont think it is correct Please help
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There's at least one mistake, maybe more - can't be sure because you've left out parentheses.
 P: 61 Thank you for your reply, (0.05^2+0.05)/(2.88/4*0.018)=r^2 this is what I had changed it to .... thanks
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## Rearrange of formula

That looks worse!
Whichever, post your individual steps, just making one simple change at a time.
 P: 61 Ok So I started with : 0.05=(2.88/4*1*0.018)(0.05^2-r^2) I wish to make r^2 the subject so , I rearrange to make ; r^2 = (0.05^2+0.05) / (2.88/4*1*0.018) As the first two parentheses are multiply I change it to a divide. I exchange r^2 with the 0.05 and used a plus instead of a minus in the formula.
 PF Patron HW Helper Sci Advisor Thanks P: 25,496 hi rad10k! some people can do these things safely in their head some people can't you can't (you get confused about where to put the brackets) you need to follow haruspex's advice … just do one operation at a time(and not just this question, but always, including in the exam, or you'll make mistakes and lose marks!)
 P: 61 This is the equation : u={∆P/4.Lμ}(R^2-r^2) and I wish to find r^2 but a unsure how to rearrange it I thought maybe; r^2=u/{∆P.Lμ}(R^2 ) ??
 PF Patron HW Helper Sci Advisor Thanks P: 25,496 why are you not following our advice? do it in steps, ie one operation at a time! the first step would be u = {∆P/4.Lμ}(R2-r2) u/{∆P/4.Lμ} = (R2-r2)
 P: 61 u = {∆P/4.Lμ}(R2-r2) u/{∆P/4.Lμ} = (R2-r2) This was arrived by dividing both sides by {∆P/4.Lμ} and cancelling on the right to leave (R2-r2) on its own . So then do I need to subtract R2 from both sides cancelling out R2 on the right leaving; u/{∆P/4.Lμ} - R2 = -r2 ? I apologise but I am rubbish at rearranging
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 Quote by rad10k I am rubbish at rearranging
But see how much better you do when you take smaller steps!
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P: 25,496
 Quote by rad10k I apologise but I am rubbish at rearranging
then you need to practise!

(caution: you'll always be a bit rubbish,

so no matter how much practice you get, and how good you think you've become,

you must always do it one step at a time, so that in the pressure of the exam:

i] you're less likely to make a mistake

ii] if you do make a mistake, at least the examiner can see it's a silly error, and only take off one mark! )
 P: 61 Thanks guys :)

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