Đáp án + Giải thích các bước giải:
`a) (3x²-2x-4)(2x+5)-(3x-4)²`
`= 6x³+15x²-4x²-10x-8x-20-9x²+24x-16`
`=6x³+2x²+6x-36`
`b) (3x²-4x-5)(4x-6)-(2x+4)(2x-4)`
`= 12x³-18x²-16x²+24x-20x+30-4x²+16`
`= 12x³-38x²+4x+46`
`c) (2x+3)³-(4x-3)(16x²+12x+9)`
`=8x³+36x²+54x+27-64x³+27`
`=-56x³+36x²+54x+54`
`d) (3x-5)³-(2x+3)²`
`= 27x³-135x²+225x-125-4x²-12x-9`
`=27x³-139x²+213x-134`
Áp dụng các HĐT:
`(a+b)^2=a^2+2ab+b^2`
`(a-b)^2=a^2-2ab+b^2`
`a^2-b^2=(a-b)(a+b)`
`(a+b)^3=a^3+3a^2b+3ab^2+b^3`
`(a-b)^3=a^3-3a^2b+3ab^2-b^3`
`a^3-b^3=(a-b)(a^2+ab+b^2)`
