Đáp án+Giải thích các bước giải:

 Bài `1` :

`a,`

 `(x+2y)^3`

`= x^3 + 3.x^2 . 2y + 3.x.(2y)^2 + (2y)^3`

`= x^3 + 6x^2 y + 12xy^2 + 8y^3`

`b,`

`(2x+3)^3`

`= (2x)^3 + 3.(2x)^2 . 3 + 3.2x.3^2 + 3^3`

`= 8x^3 + 36x^2  + 54x + 27`

`c,`

`(2x-3y)^3`

`= (2x)^3 - 3.(2x)^2 . 3y + 3.2x.(3y)^2 - (3y)^3`

`= 8x^3 - 36x^2y + 54xy^2 - 27y^3`

`d,`

`({2x}/3 - 1)^3`

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

`= 8/27 x^3 . 4/3 x^2 + 2x - 1`

`e,`

`(-2y + 3x^2)^3`

`= (-2y)^3 + 3.(-2y)^2 . 3x^2 + 3.(-2y).(3x^2)^2 + (3x^2)^3`

`= -8y^3 + 36y^2 x^2 - 54y x^4 + 27x^6`

`f,`

`({2y}/x - x/y)^3`

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

`= {8y^3}/x^3 - {12xy^2}/x^2y + {6x^2y}/{xy^2} - {x^3}/{y^3}`

`g,`

`(4x^2 + 3y)^3`

`= (4x^2)^3 + 3.(4x^2)^2 . 3y + 3.4x^2 . (3y)^2 + (3y)^3`

`= 64x^6 + 144x^4 y + 108x^2y^2 + 27y^3`

`h,`

`(5x-4y)^3`

`=(5x)^3 - 3.(5x)^2 . 4y + 3.5x.(4y)^2 - (4y)^3`

`= 125x^3 - 300x^2 y + 240 xy^2 - 64y^3`