To find the expression representing the sum of $(10x - 2)$ and $(-6x - 9)$, follow these steps:

1. Write down the original expressions: $(10x - 2) + (-6x - 9)$

2. Combine like terms:

   • Combine the $x$ terms: $10x + (-6x) = 4x$

   • Combine the constant terms: $-2 + (-9) = -11$

3. Write the simplified expression: $4x - 11$

So, the expression that represents the sum in simplest terms is $\boxed{4x - 11}$.

Would you like further explanation or examples? Here are some related questions:

1. How would the expression change if the second term was positive, $6x + 9$?
2. Can you factor the expression $4x - 11$?
3. What happens if $x = 2$? What is the value of the expression?
4. How does the expression relate to a linear equation?
5. What is the derivative of the expression $4x - 11$ with respect to $x$?

Tip: When combining expressions, always pay close attention to the signs (positive or negative) in front of each term.