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Đáp án+Giải thích các bước giải:

 `1)(x-1).(x^{2}+x+1)-x.(x+2).(2-x)=5`

`(x-1).(x^{2}+x.1+1^{2})-x.(x+2).(x-2)=5`

`x^{3}-1^{3}-x.(x^{2}-2^{2})=5`

`x^{3}-x^{3}+4x-1=5`

`4x=6`

`x=3/2`

Vậy `x=3/2`

`3)(x+1).(x^{2}-x+1)-x.(x-2).(x+2)=21`

`(x+1).(x^{2}-x.1+1^{2})-x.(x^{2}-2^{2})=21`

`x^{3}+1^{3}-x^{3}+4x=21`

`4x+1=21`

`4x=20`

`x=5`

vậy `x=5`

`5)(x-1)^{3}-(x+3).(x^{2}-3x+9)+3.(x^{2}-4)=2`

`(x^{3}-3.x^{2}.1+3.x.1^{2}-1^{3})-(x+3).(x^{2}-x.3+3^{2})+3x^{2}-12=2`

`x^{3}-3x^{2}+3x-1-(x^{3}+3^{3})+3x^{2}=14`

`x^{3}-x^{3}-3x^{2}+3x^{2}+3x-1-27=14`

`3x=14+1+27`

`3x=42`

`x=14`

Vậy `x=14`