Đáp án:
Câu 3) sai đề nên không làm được tiếp.
Giải thích các bước giải:
`a)(x^2-1)^3-(x^4+x^2+1)(x^2-1)`
`=(x^2-1)(x^2-1)^2-(x^2-1)(x^4+x^2+1)`
`=(x^2-1)(x^4-2x^2+1)-(x^2-1)(x^4+x^2+1)`
`=(x^2-1)(x^4-2x^2+1-x^4-x^2-1)`
`=-3x^2(x^2-1)`
`=-3x^4+3x^2`
`b)(x^4-3x^2+9)(x^2+3)-(3+x^2)^3`
`=(x^4-3x^2+9)(x^2+3)-(x^2+3)(x^2+3)^2`
`=(x^4-3x^2+9)(x^2+3)-(x^2+3)(x^4+6x^2+9)`
`=(x^2+3)(x^4-3x^2+9-x^4-6x^2-9)`
`=-9x^2(x^2+3)`
`=-9x^4-27x^2`
`c)(x-3)^3-(x-3)(x^2+3x+9)+6(x+1)^2`
`=x^3-9x^2+27x-27-(x^3-3^3)+6(x^2+2x+1)`
`=x^3-9x^2+27x-27-x^3+27+6x^2+12x+6`
`=-3x^2+39x+6`
`2)`
`A=(x+1)(x-1)(x^2+x+1)(x^2-x+1)(x=-3)`
`=(x^2-1)[(x^2+1)^2-x^2]`
`=(x^2-1)(x^4+2x^2+1-x^2)`
`=(x^2-1)(x^4+x^2+1)`
`x=-3=>x^2=9,x^4=81`
`=>A=(9-1)(81+9+1)`
`=>A=8.91=728`
`3)`
`(x+3)^2-(3x+1)^2+(2x+1)(4x^2-2x+1)=28`
`<=>x^2+6x+9-(9x^2+6x+1)+(2x)^3+1^3=28`
`<=>-8x^2+9+8x^3=28`
`<=>8x^3-8x^2-19=0`