To distribute the $-9$ over the expression $(x + 1)$, apply the distributive property. This involves multiplying $-9$ by each term inside the parentheses:

$-9(x + 1) = -9 \cdot x + (-9) \cdot 1$

Now, simplify:

$-9(x + 1) = -9x - 9$

Thus, the expression simplifies to:

$-9x - 9$

Would you like more details or further explanation on any of the steps?

Here are 5 related questions to expand your understanding:

1. How do you factor an expression like $-9x - 9$ back into its original form?
2. What is the distributive property in mathematics?
3. How would this change if the expression were $-9(x - 1)$?
4. What happens if we distribute a positive number instead of a negative one?
5. How does the distributive property apply in real-world scenarios?

Tip: Always remember to distribute the negative sign along with the number when dealing with negative coefficients.