Solve for q 1/p + 1/q = 1/f

[cmdrox]

1/p + 1/q = 1/f

How do I solve for q?

 

[ilaggoodly]

subtract and invert?
1/q = 1/f - 1/p
so q = (1/f-1/p)^-1

 

[Mrspi]

1/p + 1/q = 1/f

How do I solve for q?

This might be easier if it had no fractions. So, multiply both sides by the least common denominator for all the fractions, pqf:

pqf * (1/p) + pqf * (1/q) = pqf * (1/f)

qf + pf = pq

Ok...you're supposed to solve for q. Get all terms containing "q" on one side of the equals sign, and everything else on the other side....

I'll let you take it from here. If you still have trouble, repost showing everything you've done to try to solve the problem.

 

[cmdrox]

Wow, that helps a lot. I understand it now, thanks!

 

[Denis]

or you can go this way (my favorite):

1/q = 1/f - 1/p

1/q = (p-f) / (fp)

q = fp / (p-f)