Đáp án:
Giải thích các bước giải:
3) `(3x+1)^2-4(x-2)^2`
`=(3x+1)^2-[2(x-2)]^2`
`=[(3x+1)-2(x-2)].[(3x+1)+2(x-2)]`
`=(3x+1-2x+4)(3x+1+2x-4)`
`=(x+5)(5x-3)`
4) `9(2x+3)^2-4(x-2)^2`
`=[3(2x+3)]^2-[4(x-2)]^2`
`=[3(2x+3)-2(x-2)].[3(2x+3)+2(x-2)]`
`=(6x+9-2x+4)(6x+9+2x-4)`
`=(4x+13)(8x+5)`