Simplify 3x^2+6-2x+5x-4x^2+9

3 x² + 6 - 2 x + 5 x - 4 x² + 9 =

3 x² - 4 x² - 2 x + 5 x + 6 + 9 =

- x² + 3 x + 15 = - ( x² - 3 x - 15 )

To simplify the expression 3x^2 + 6 - 2x + 5x - 4x^2 + 9, you need to combine like terms.

First, rewrite the expression in terms of like terms:
(3x^2 - 4x^2) + (5x - 2x) + (6 + 9)

Next, combine the like terms separately:
- x^2 + 3x + 15

So, the simplified form of the expression 3x^2 + 6 - 2x + 5x - 4x^2 + 9 is -x^2 + 3x + 15.