# algebra

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Rearrange r+s/8s=r-s/8n to make r the subject.

OK, I have started by rearranging the formula:

8n(r+s)=8s(r-s)

What do I do next?

• algebra -

so you must have meant
(r+s)/(8s)=(r-s)/(8n)

so 8n(r+s)=8s(r-s) is correct so far. Le'ts expand it
8nr + 8rs = 8rs - 8s^2
8nr = -8s^2
nr = -s^2
r = -s^2/n

• algebra -

thank you!

• algebra -

just realised, should the second line be
8nr+8NS?, not 8rs?

• algebra -

just realised, should the second line be
8nr+8NS?, not 8rs?.........

• algebra -

your are right, good for you to notice
I have to mind my n, r and s's

8nr + 8ns = 8rs - 8s^2
collect all terms containing r to one side
8nr - 8rs = -8s^2 - 8ns
factor out the r
r(8n - 8s) = -8s^2 - 8ns
r = (-8s^2 - 8ns)/(8n - 8s)
divide top and bottom by 8 on the RS
r = (-s^2 - ns)/(n-s)
or -s(s+n)/(n-s)

• algebra -

great, that makes sense, thanks

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