1. **Stating the problem:** You asked which numbers can be used in synthetic division. 2. **Explanation:** Synthetic division is a shortcut method used to divide a polynomial by a binomial of the form $x - c$. 3. **Key point:** The number used in synthetic division is the root or zero of the divisor polynomial. 4. **Details:** For a divisor $x - c$, the number used in synthetic division is $c$. 5. **Example:** If dividing by $x - 3$, the number used is $3$. 6. **General rule:** You can only use numbers corresponding to linear factors of the form $x - c$. For other forms, synthetic division isn't directly applicable. 7. **Summary:** The numbers used in synthetic division are the constants $c$ from divisors $x - c$.