$$\frac { 1 } { a } = \frac { 1 } { b } + \frac { 1 } { c }$$
$a=\frac{bc}{b+c}$
$c\neq 0\text{ and }b\neq 0\text{ and }b\neq -c$
$b=-\frac{ac}{a-c}$
$c\neq 0\text{ and }a\neq 0\text{ and }a\neq c$