Answer
$$\frac{ab}{b+a}$$
Work Step by Step
Simplifying the given expression using the rules of radicals/exponents, we find:
$$\frac{1}{\left(a^{-1}+b^{-1}\right)} \\ \frac{1}{\frac{1}{a}+\frac{1}{b}}\\ \frac{1}{\frac{b+a}{ab}} \\ \frac{ab}{b+a}$$
