Đáp án:
1. (2x-3y)(4x^2+6xy+9y^2)
=(2x-3y){(2x)^2+2x*3y+(3y)^2}
Ta coi 2x=a;3y=b => no tro thanh
(a-b)(a^2+ab+b^2)
=a^3-b^3
2.(x+3)(x^2-3x+9)
La hang dang thuc : x^3+3^3 =x^3+27=-2^3+27=27-8=19
3.(x-2)(2+x)=(x-2)(x+2)=x^2-2^2=x^2-4 (hang dang thuc so ba)
4.(x+3)(2x-3)-2x^2+9
=2x^2-3x+6x-9-2x^2+9
=3x