Đáp án:
`a)A=-6x²-2`
`b)B=2x³+6xy²`
`c)C=x³-y³`
`d)D=64`
Giải thích các bước giải:
`a)A=(x-1)³-(x+1)³`
`=x³-3x²+3x-1-(x³+3x²+3x+1)`
`=x³-3x²+3x-1-x³-3x²-3x-1`
`=(x³-x³)-(3x²+3x²)+(3x-3x)-(1+1)`
`=-6x²-2`
`b)B=(x+y)³+(x-y)³`
`=x³+3x²y+3xy²+y³+x³-3x²y+3xy²-y³`
`=(x³+x³)+(3x²y-3x²y)+(3xy²+3xy²)+(y³-y³)`
`=2x³+6xy²`
`c)C=(x-y)³+3xy(x-y)`
`=x³-3x²y+3xy²-y³+3x²y-3xy²`
`=x³+(-3x²y+3x²y)+(3xy²-3xy²)-y³`x
`=x³-y³`
`d)D=(x+1)³+(x-3)³-2(x²+15)(x-3)`
`=x³+3x²+3x+1+x³-9x²+27x-27-2(x³-3x²+15x-45)`
`=x³+3x²+3x+1+x³-9x²+27x-27-2x³+6x²-30x+90`
`=(x³+x³-2x³)+(3x²-9x²+6x²)+(3x+27x-30x)+(1-27+90)`
`=64`
