Hướng dẫn trả lời:
1. `(x + 3y)^2 = x^2 + 2.x.3y + (3y)^2 = x^2 + 6xy + 9y^2.`
2. `(5x - y)^2 = (5x)^2 - 2.5x.y + y^2 = 25x^2 - 10xy + y^2.`
3. `(2x + y)^3 = (2x)^3 + 3.(2x)^2.y + 3.2x.y^2 + y^3`
`= 8x^3 + 12x^2y + 6xy^2 + y^3.`
4. `(3x – 2y)^3 = (3x)^3 - 3.(3x)^2 .2y + 3.3x.(2y)^2 - (2y)^3`
`= 27x^3 - 54x^2y + 36xy^2 - 8y^3.`
5. `(x + 4).(x^2 – 4x + 16) = (x + 4).(x^2 - x.4 + 4^2) = x^3 + 4^3`
`= x^3 + 64.`
6. `(x - 3).(x + 3) = x^2 - 3^2 = x^2 - 9.`
7. `(x + 3).(x^2 - 3x + 9) = (x + 3).(x^2 - x.3 + 3^2) = x^3 + 3^3`
`= x^3 + 27.`