Posted by **Sab** on Tuesday, August 28, 2012 at 10:48am.

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 -
**Reiny**, Tuesday, August 28, 2012 at 11:02am
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 -
**Sab**, Tuesday, August 28, 2012 at 11:05am
thank you!

- algebra -
**Sab**, Tuesday, August 28, 2012 at 11:10am
just realised, should the second line be

8nr+8NS?, not 8rs?

- algebra -
**Sab**, Tuesday, August 28, 2012 at 11:15am
just realised, should the second line be

8nr+8NS?, not 8rs?.........

- algebra -
**Reiny**, Tuesday, August 28, 2012 at 11:18am
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 -
**Sab**, Tuesday, August 28, 2012 at 11:23am
great, that makes sense, thanks

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