Đáp án:
`a)x=2`
`b)x=-3`
Giải thích các bước giải:
`a)(2x-1)(4x²+2x+1)-8x.(x²-1)=15`
`⇔(2x-1)[(2x)²+2x.1+1²]-8x³+8x=15`
`⇔(2x)³-1³-8x³+8x=15`
`⇔8x³-1-8x³+8x=15`
`⇔8x-1=15`
`⇔8x=15+1`
`⇔8x=16`
`⇔x=16:8`
`⇔x=2`
Vậy `x=2`
`b)(x-1)(x²+x+1)-(2+x)(4-2x+x²)=3x`
`⇔(x-1)(x²+x.1+1²)-(2+x)(2²-2.x+x²)=3x`
`⇔x³-1³-(2³+x³)=3x`
`⇔x³-1-(8+x³)=3x`
`⇔x³-1-8-x³=3x`
`⇔x³-x³-3x=1+8`
`⇔-3x=9`
`⇔x=9:(-3)`
`⇔x=-3`
Vậy `x=-3`