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Rearranging equations help, GCSEs were a decade ago watch

1. Hello,

I went back into education after a while away and I need help with rearranging equations. Here is the example I'm trying to rearrange:
R/r = sqrt(f+p)/(f-p)
Attachment 694548
I need to rearrange for f.

So far this is what I've done:

I have tried to move forward in various ways and none of them work. I actually managed to get rid of f somehow which is clearly not ideal. Any help would be appreciated but I really need some detailed advice. I can't continue to spend hours rearranging things and getting nowhere.
2. Next multiply both sides by r^2. Expand the brackets, then collect f terms on one side of the equals sign.

Let me know if u have any more questions or need further help
3. (Original post by whatever24)
So far this is what I've done:

I could be missing something here but you've literally done it? now all you have to do is subtract p from both sides and you have f on it's own = the rest of the equation ???????
4. (Original post by econflower)
I could be missing something here but you've literally done it? now all you have to do is subtract p from both sides and you have f on it's own = the rest of the equation ???????
Assuming the OP need some to make f the subject, you can't have f on both sides of the equation.
5. (Original post by Notnek)
Assuming the OP need some to make f the subject, you can't have f on both sides of the equation.
How did i manage to miss seeing the f on the left?! haha my bad
6. from what you've done
7. f =[p(r^2+R^2)]/(R^2-r^2)
8. Thank you everyone! Thank you for replying so quickly as well
9. A reminder to everyone : full solutions are not allowed in the maths forum. Please read the posting guidelines at the top of the forum. Thanks.

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