~ Bạn tham khảo ~
`a, 8x^3 + 36x^2 + 54x + 27`
`= (2x)^3 + 3*(2x)^2*3 + 3*2x+3^2 + 3^3`
`= (2x+3)^3`
`b, 27a^3 - 27a^2 + 9a - 1`
`= (3a)^3 - 3*(3a)^2*1 + 3*3a*1^3 - 1^3`
`= (3a-1)^3`
`c, (a+2b)^3 - (a+2b)(a^2-2ab+4b^2)`
`= a^3 + 6a^2b + 12ab^2 + 8b^3 - a^3-8b^3`
`= 6a^2b + 12ab^2`
`d, (x-2y)^3 + 6xy(x-2y)-x^3`
`= x^3-6x^2y+12xy^2-8y^3 + 6x^2y-12xy^2-x^3`
`= -8y^3`
