## College Algebra (6th Edition)

$f=\frac{pq}{q+p}$
Multiply all terms by the LCD. Then factor out $f$ from $qf+pf$ and divide both sides by $q+p$. $\frac{1}{p}+\frac{1}{q}=\frac{1}{f}$ for $f$ $pqf(\frac{1}{p}+\frac{1}{q})=\frac{1}{f}(pqf)$ $qf+pf=pq$ $f(q+p)=pq$ $f=\frac{pq}{q+p}$