(4x2–5x+9)+(–7x2–10x+6).

Sure, let's solve this step by step:

1. First, let's group the like terms together. Like terms are those terms which have the same variable raised to the same power. Here, the like terms are 4x^2 and -7x^2, -5x and -10x, and 9 and 6.

2. Add the coefficients of the like terms:

   For x^2 terms: 4x^2 - 7x^2 = -3x^2 For x terms: -5x - 10x = -15x For constant terms: 9 + 6 = 15

3. Now, combine these results to get the final answer:

   -3x^2 - 15x + 15

So, the simplified form of the expression "(4x^2–5x+9)+(–7x^2–10x+6)" is "-3x^2 - 15x + 15".