1. The problem is to find the reciprocal of a given number or expression. 2. The reciprocal of a number $x$ is defined as $\frac{1}{x}$, provided $x \neq 0$. 3. Important rule: Multiplying a number by its reciprocal always gives 1, i.e., $x \times \frac{1}{x} = 1$. 4. For example, if the number is $5$, its reciprocal is $\frac{1}{5}$. 5. If the number is a fraction like $\frac{a}{b}$, its reciprocal is $\frac{b}{a}$, assuming $a \neq 0$. 6. Always check that the original number is not zero because the reciprocal of zero is undefined. Final answer: The reciprocal of a number $x$ is $\frac{1}{x}$.