Simplify (-3d^2-8+2d)+(4d-12+d^2)

$(- 3 d^{2} - 8 + 2 d) + (4 d - 12 + d^{2})$

Remove parentheses.

$- 3 d^{2} - 8 + 2 d + 4 d - 12 + d^{2}$

Add $- 3 d^{2}$ and $d^{2}$ .

$- 2 d^{2} - 8 + 2 d + 4 d - 12$

Subtract $12$ from $- 8$ .

$- 2 d^{2} + 2 d + 4 d - 20$

Add $2 d$ and $4 d$ .

$- 2 d^{2} + 6 d - 20$