Đáp án+Giải thích các bước giải:
Bài 2:
Sửa đề:
`K=8x^3+12x^2y+6xy^2+y^3`
`\to K=8x^3+3.4x^{2}.y+3.2x.y^2+y^3`
`\to K=(2x)^3+3.(2x)^{2}.y+3.2x.y^2+y^3`
`\to K=(2x+y)^3`
Bài 3:
$a/$
`3(x-1)^3+(x+2)(x-2)-(x-1)(x+1)`
`=3(x^3-3x^2+3x-1)+(x^2-4)-(x^2-1)`
`=3x^3-9x^2+9x-3+x^2-4-x^2+1`
`=3x^3-9x^2+9x-3-3`
`=3x^3-9x^2+9x-6`
$b/$
`(3x+2)^3+(x+1)^2`
`=(3x)^3+3.(3x)^{2}.2+3.3x.2^2+2^3+(x^2+2x+1)`
`=27x^3+3.9x^{2}.2+3.3x.4+8+(x^2+2x+1)`
`=27x^3+54x^2+36x+8+x^2+2x+1`
`=27x^3+55x^2+38x+9`
$c/$
`(x-3)^3+(x+3)^3`
`=x^3-3x^{2}.3+3.x.3^2-3^3+(x^3+3x^{2}.3+3.x.3^2+3^3)`
`=x^3-9x^2+27x-27+x^3+9x^2+27x+27`
`=(x^3+x^3)+(-9x^2+9x^2)+(27x+27x)+(-27+27)`
`=2x^3+54x`
