Rearrange of formula

rad10k

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

haruspex

There's at least one mistake, maybe more - can't be sure because you've left out parentheses.
Please post your individual individual steps, using parentheses as appropriate.

rad10k

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

haruspex

That looks worse!
You start with 0.05=(2.88/4*1*0.018)(0.05²-r²). Do you mean 0.05=(2.88/(4*1*0.018))(0.05²-r²) or 0.05=((2.88/4)*1*0.018)(0.05²-r²)?
Whichever, post your individual steps, just making one simple change at a time.

rad10k

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.

tiny-tim

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!)

rad10k

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 ) ??

tiny-tim

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)

rad10k

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

haruspex

But see how much better you do when you take smaller steps!

tiny-tim

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! )

rad10k

Thanks guys :)