Simplify (8x-4-4x^2)+(7x^2-9x-6)

$(8 x - 4 - 4 x^{2}) + (7 x^{2} - 9 x - 6)$

Remove parentheses.

$8 x - 4 - 4 x^{2} + 7 x^{2} - 9 x - 6$

Subtract $9 x$ from $8 x$ .

$- 4 - 4 x^{2} + 7 x^{2} - x - 6$

Subtract $6$ from $- 4$ .

$- 4 x^{2} + 7 x^{2} - x - 10$

Add $- 4 x^{2}$ and $7 x^{2}$ .

$3 x^{2} - x - 10$