Bài tập 6 :

`a, (7x -3)(2x^2 +x -8)`

`= 7x (2x^2 +x -8) -3(2x^2 +x -8)`

`= 14x^3 +7x^2 -56x -6x^2 -3x +24`

`= 14x^3 +x^2 -59x +24`

`b, (4x+1)(x^2-x+6)`

`= 4x(x^2-x+6) + (x^2-x+6)`

`= 4x^3 -4x^2 +24x +x^2 -x+6`

`= 4x^3 -3x^2 +23x +6`

`c, (3x-5)(2x^2 +7x-3)`

`= 3x(2x^2 +7x-3) -5(2x^2 +7x-3)`

`= 6x^3 +21x^2 -9x -10x^2 -35x +15`

`= 6x^3 +11x^2- 44x +15`

Bài tập 7 :

`a, D(x) = x(x+3) +2(x-1)`

`D(x) = x^2 +3x +2x-2`

`D(x) = x^2 +5x-2`

`b, E(x) = 2x(x-4) +5(x+2)`

`E(x) = 2x^2 -8x +5x +10`

`E(x) = 2x^2 -3x+10`

`c, F(x) = x(x-1) +4(x+3)`

`F(x) = x^2-x+4x+12`

`F(x) =x^2 +3x+12`

`d, H(x) = x(x-4) +3(x+2)`

`H(x)=x^2-4x+3x+6`

`H(x) =x^2 -x+6`

Bài tập 8 :

`a, A(x)=(3x+2)(x-5) +4x^2 -6`

`A(x) = 3x(x-5)+2(x-5)+4x^2 -6`

`A(x) = 3x^2 -15x +2x-10 +4x^2 -6`

`A(x) = 7x^2 -13x-16`

`b, B(x)=(x-1)(2x+3) +7x^2 -2x+1`

`B(x)=x(2x+3)-(2x+3) +7x^2 -2x+1`

`B(x)=2x^2 +3x -2x-3+7x^2 -2x+1`

`B(x)=9x^2 -x-2`

`c, C(x)=(x+4)(x-2) +3x^2 -5x+6`

`C(x)=x(x-2) +4(x-2) +3x^2 -5x +6`

`C(x)=x^2 -2x +4x -8 +3x^2 -5x +6`

`C(x) = 4x^2 -3x-2`

`d, G(x)=(2x-1)(x+3) +4x^2 -5x +7`

`G(x) = 2x(x+3) -(x+3) +4x^2 -5x +7`

`G(x) = 2x^2 +6x -x-3 +4x^2 -5x+7`

`G(x) = 6x^2 +4`