`1,-5x(x-3)(2x+4)-(x+7)(x-3)+(5x-2)(3x+4)`

`=-5x(2x^2-2x-12)-(x^2+4x-21)+15x^2+14x-8`

`=-10x^3+10x^2+60x-x^2-4x+21+15x^2+14x-8`

`=-10x^3+24x^2+70x+13`

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

`=12x^2+x-1-5x^3+15x^2-x^2+7x-12-7x^3+14x^2-7x+7`

`=-12x^3+40x^2+x-6`

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

`=4x^3-8x^2+12x-3x(x^2-x-2)-2x^2+9x+35-4x^3+4x^2-4x`

`=4x^3-8x^2+12x-3x^3+3x^2+6x-2x^2+9x+35-4x^3+4x^2-4x`

`=-3x^3-3x^2+23x+35`

`4,5x^2(x-7)-4x(x-2)(x+3)-(x-5)(x+6)+(2x-1)(x+5)`

`=5x^3-35x^2-4x(x^2+x-6)-x^2-x+30+2x^2+9x-5`

`=5x^3-35x^2-4x^3-4x^2+24x-x^2-x+30+2x^2+9x-5`

`=x^3-38x^2+32x+25`

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

`=3x^2+2x-21+5x^3-10x^2-20x-x(4x^2-21x+20)-x^2-3x-2`

`=3x^2+2x-21+5x^3-10x^2-20x-4x^3+21x^2-20x-x^2-3x-2`

`=x^3+13x^2-41x-23`

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

`=-14x^3+28x^2+35x+2x^2-13x+15+3x^2+10x-8-4x^3-12x^2`

`=-18x^3+21x^2+32x+7`

`7,(x-6)(3x-1)-2x^2(x-2)+x(x-1)(2x+3)-5x(x^2+4x+1)`

`=3x^2-19x+6-2x^3+4x^2+x(2x^2+x-3)-5x^3-20x^2-5x`

`=3x^2-19x+6-2x^3+4x^2+2x^3+x^2-3x-5x^3-20x^2-5x`

`=-5x^3-12x^2-27x+6`

`8,(8x-1)(2x-3)-(-x+7)(x-2)-6x(x^2-x+3)+(x^2-3)(x-4)`

`=16x^2-26x+3+x^2-9x+14-6x^3+6x^2-18x+x^3-4x^2-3x+12`

`=-5x^3+19x^2-56x+29`

`9,(-3x+4)(x-2)-x(x^2-2)(-4x+1)+(2x-5)(x^2-4x)`

`=-3x^2+10x-8-x(-4x^3+x^2+8x-2)+2x^3-13x^2+20x`

`=-3x^2+10x-8+4x^4-x^3-8x^2+2x+2x^3-13x^2+20x`

`=4x^4+x^3-24x^2+32x-8`

`10,(5x-2)(x+1)-3x(x^2-x-3)-2x(x-5)(x+4)+5x(x^2-7)`

`=5x^2+3x-2-3x^3+3x^2+9x-2x(x^2-x-20)+5x^3-35x`

`=5x^2+3x-2-3x^3+3x^2+9x-2x^3+2x^2+40x+5x^3-35x`

`=10x^2+17x-2`

`11,-3x^2(x-4)+2x(x-1)(-2x+3)-(x-9)(-2x+1)-5(x-1)(x+2)`

`=-3x^3+12x^2+2x(-2x^2+5x-3)-2x^2-19x+9-5(x^2+x-2)`

`=-3x^3+12x^2-4x^3+10x^2-6x-2x^2-19x+9-5x^2-5x+10`

`=-7x^3+15x^2-30x+19`

`12,(-2x^2+5)(x-6)-4x(x^2-7x+2)-2x(x+3)(x-2)-(x^3-x^2)`

`=-2x^3+12x^2+5x-30-4x^3+28x^2-8x-2x(x^2+x-6)-x^3+x^2`

`=-2x^3+12x^2+5x-30-4x^3+28x^2-8x-2x^3-2x^2+12x-x^3+x^2`

`=-9x^3+39x^2+9x-30`

`13,(x^2-3x)(-5x^2+x)-x^3(x-7)+5x^2(x-2)(x-4)-(x+1)(x+3)`

`=-5x^4+16x^3-3x^2-x^4+7x^3+5x^2(x^2-6x+8)-x^2-4x-3`

`=-5x^4+16x^3-3x^2-x^4+7x^3+5x^4-30x^3+40x^2-x^2-4x-3`

`=-x^4-7x^3+36x^2-4x-3`

`14, (-x+4)(x-5)-7x(x^2-5x+2)+(-5x+1)(x^2-5)+30`

`=-x^2+9x-20-7x^3+35x^2-14x-5x^3+x^2+25x-5+30`

`=-12x^3+35x^2+20x+5`

`15,3x(x-2)(x+2)-2x(x-3)(x-7)+(x-1)(x^2-2x+2)`

`=3x(x^2-4)-2x(x^2-10x+21)+x^3-3x^2+4x-2`

`=3x^3-12x-2x^3+20x^2-42x+x^3-3x^2+4x-2`

`=2x^3+17x^2-50x-2`

`16,(x-3)(x^2-3x)-(4x-2)(-x^2+1)-4x(x-7)(x+1)-(x^2-x-1)`

`=x^3-6x^2+9x+4x^3-2x^2-4x+2-4x(x^2-6x-7)-x^2+x+1`

`=x^3-6x^2+9x+4x^3-2x^2-4x+2-4x^3+24x^2+28x-x^2+x+1`

`=x^3+15x^2+34x+3`

`17,-7x(x+2)(x-3)+5x(-2x^2+x-4)+3x(x^2-5x-7)-(x^2-5x)`

`=-7x(x^2-x-6)-10x^3+5x^2-20x+3x^3-15x^2-21x-x^2+5x`

`=-7x^3+7x^2+42x-10x^3+5x^2-20x+3x^3-15x^2-21x-x^2+5x`

`=-14x^3-4x^2+6x`

`18,10(x^2-x+1)-(x-5)(2x+1)+5x(x-3)-(-7x^2+4x-5)`

`=10x^2-10x+10-2x^2+9x+5+5x^2-15x+7x^2-4x+5`

`=20x^2-20x+20`

`19,-5x(-2x^2+4x-10)+(4x^2-2x)(-3x+1)-(-9x^3+2x^2-x)`

`=10x^3-20x^2+50x-12x^3+10x^2-2x+9x^3-2x^2+x`

`=7x^3-12x^2+49x`

`20,7x^2-(-3x^2+4x-15)+(2x-1)(-3x-2)-(x-4)(x+5)`

`=7x^2+3x^2-4x+15-6x^2-x+2-x^2-x+20`

`=3x^2-6x+37`

Đáp án:

Giải thích các bước giải:

 1) -5x(x-3)(2x+4) - (x+7)(x-3) + (5x-2)(3x+4)

=(-5x²+15x)(2x+4) - x²+3x-7x+21+15x²+20x-6x-8

=-10x³-20x²+30x²+60x+14x²+10x+13

=-10x³+24x²+70x+13

  2) (4x-1)(3x+1)-5x²(x-3)-(x-4)(x-3)-7(x³-2x²+x-1

=42x²+4x-3x-1-5x³+15x²-x²+3x+4x-12-7x³+14x²-7x+7

=(-5x³-7x³)+(42x²+15x²-x²+14x²)+(4x-3x+3x+4x-7x)+(-1-12+7)

=-12x³+70x²+x-6