Đáp án+Giải thích các bước giải:
Bài 1:
`a) (x+1)^3-x(x-2)^2-1`
`=x^3+3.x^2.1+3.x.1+1^3-x(x^2-4x+4)-1`
`=x^3+3x^2+3x+1-x^3+4x^2-4x-1`
`=7x^2-x`
`b) (x+1)(x^2+x+1)(x-1)(x^2-x+1)`
`=[(x+1)(x^2+x+1)].[(x-1)(x^2-x+1)]`
`=(x^3+1)(x^3-1)`
`=(x^3)^2-1^1`
`=x^6-1`
`c) (2a+1)^3`
`=(2a)^3+3.(2a)^2.1+3.2a.1^2+1^3`
`=8a^3+3.4a+6a+1`
`=8a^3+12a+6a+1`
`=8a^3+18a+1`
`d) (3a-2b)^3`
`=(3a)^3-3.(3a)^2 .2b+3.3a.(2b)^2-(2b)^3`
`=27a^3-3.9a^2 .2b+3.3a.4b^2-8b^3`
`=27a^3-54a^2b+36ab^2-8b^3`
