Đáp án+Giải thích các bước giải:

Bài `1`: 

`a)A=(x-5).(x^{2}+5x+25)-x^{3}+2`

`=x.(x^{2}+5x+25)-5.(x^{2}+5x+25)-x^{3}+2`

`=(x^{3}+5x^{2}+25x-5x^{2}-25x-125)-x^{3}+2`

`=x^{3}-125-x^{3}+2`

`=-123`

Vậy `A=-123`

`b)B=(4x^{2}+2x+1).(2x-1)-8.(x^{3}+1)`

`=(8x^{3}-4x^{2}+4x^{2}-2x+2x-1)-8x^{3}-8`

`=8x^{3}-1-8x^{3}-8`

`=-9`

Vậy `B=-9`

`c)C=x.(5x-3)-x^{2}.(x-1)+x.(x^{2}-6x)+3x-10`

`=5x^{2}-3x-x^{3}+x^{2}+x^{3}-6x^{2}+3x-10`

`=(x^{3}-x^{3})+(5x^{2}+x^{2}-6x^{2})+(3x-3x)-10`

`=-10`

Vậy `C=-10`

`d)D=(2x+1).x-x^{2}.(x+2)+x^{3}-x+3`

`=2x^{2}+x-x^{3}-2x^{2}+x^{3}-x+3`

`=(x^{3}-x^{3})+(2x^{2}-2x^{2})+(x-x)+3`

`=3`

Vậy `D=3`

`e)E=5x.(x^{2}-7x+2)-x^{2}.(5x-8)+27x^{2}-10x+2`

`=5x^{3}-35x^{2}+10x-5x^{3}+8x^{2}+27x^{2}-10x+2`

`=(5x^{3}-5x^{3})+(-35x^{2}+8x^{2}+27x^{2})+(10x-10x)+2`

`=2`

Vậy `E=2`