Answer:
[tex]-20x^2+5x-6\\[/tex]
Step-by-step explanation:
Start by removing the grouping symbols (parentheses) using the sign rules:
[tex](-5x^2+2x+6)-(9x^2+2x+9)+(-6x^2+5x-3)=\\=-5x^2+2x+6-9x^2-2x-9-6x^2+5x-3[/tex]
Then we re-order and combine like terms:
[tex]-5x^2+2x+6-9x^2-2x-9-6x^2+5x-3=\\=-5x^2-9x^2-6x^2+2x-2x+5x+6-9-3=\\=-20x^2+5x-6[/tex]
