Đáp án + Giải thích các bước giải:
`b)` `9x^2-(3x-4)^2`
`=(3x)^2-(3x-4)^2`
`=[3x-(3x-4)][3x+(3x-4)]`
`=(3x-3x+4)(3x+3x-4)`
`=4(6x-4)=24x-16`
`d)` `(a^2+2a+3)(a^2+2a-3)`
`=(a^2+2a)^2-3^2`
`=a^4+4a^3+4a^2-9`
`f)` `(y+2z-3)(y-2z-3)`
`=(y-3+2z)(y-3-2z)`
`=(y-3)^2-(2z)^2`
`=y^2-6y+9-4z^2`
`g)` `(3y+4)(9y^2-12y+16)`
`=(3y+4)[(3y)^2-3y*4+4^2]`
`=(3y)^3+4^3=27y^3+64`
`j)` `(x+y)^3-(x-y)^3`
`=[(x+y)-(x-y)][(x+y)^2+(x+y)(x-y)+(x-y)^2]`
`=(x+y-x+y)(x^2+2xy+y^2+x^2-y^2+x^2-2xy+y^2)`
`=2y(3x^2+y^2)=6x^2y+2y^3`.
