`a)` `5x(x^3-1/2x^2-1)`
`=5x.x^3 -5x. 1/2x^2-5x.1`
`=5x^4-5/2x^3-5x`
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`b)` `(2x-1)(3x^2+5x-1/2)`
`=2x(3x^2+5x-1/2)-1.(3x^2+5x-1/2)`
`=6x^3+10x^2-x-3x^2-5x+1/2`
`=6x^3+7x^2-6x+1/2`
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`c)` `(x-2)^3`
`=x^3 -3x^2 .2+3.x.2^2 -2^3`
`=x^3-6x^2+12x-8`
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`d)` `8x^3-y^3`
`=(2x)^3-y^3`
`=(2x-y)[(2x)^2+2x.y+y^2]`
`=(2x-y)(4x^2+2xy+y^2)`
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`e)` `9x^2-4y^2`
`=(3x)^2-(2y)^2`
`=(3x+2y)(3x-2y)`
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`f)` `(x^2-4)^2`
`=(x^2)^2-2x^2 .4+4^2`
`=x^4-8x^2+16`
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`g)` `(x-2y)^2`
`=x^2-2x.(2y)+(2y)^2`
`=x^2-4xy+4y^2`
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`h)` `(3x+y^2)^3`
`=(3x)^3+3.(3x)^2.y^2+3x.(y^2)^2+(y^2)^3`
`=27x^3+27x^2y^2+3xy^4+y^6`
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`i)` `343-x^3`
`=7^3-x^3`
`=(7-x)(7^2+7.x+x^2)`
`=(7-x)(49+7x+x^2)`
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`k)` `(x-1)^2-(x+1)^2`
`=[(x-1)+(x+1)].[(x-1)-(x+1)]`
`=2x.(-2)`
`=-4x`
Hoặc: `(x-1)^2-(x+1)^2`
`=x^2-2x+1-(x^2+2x+1)`
`=x^2-x^2-2x-2x+1-1`
`=-4x`
