Đáp án+Giải thích các bước giải:
Bài 7:
`a)x^3+3x^2+3x+1=(x+1)^3`
`b)x^3+6x^2+8+12x`
`=x^3+6x^2+12x+8`
`=(x+2)^3`
`c)-27x+27+9x^2-x^3`
`=27-27x+9x^2-x^3`
`=(3-x)^3`
`d)8x^3+1/8+6x^2+3/2x`
`=8x^3+6x^2+3/2x+1/8`
`=(2x+1/2)^3`
`e)y^3-6y^2z-8z^3+12yz^2`
`=y^3-6y^2z+12yz^2-8z^2`
`=(y-2z)^3`
`f)(x+y)^3 .(x-y)^3`
`=[(x+y)(x-y)]^3`
`=(x^2-y^2)^3`
Bài8:
`a)(x+3)(x^2-3x+9)-(54+x^3)`
`=x^3+27-54-x^3`
`=-27`
`b)(2x+y)(4x^2-2xy+y^2)-(2x-y)(4x^2+2xy+y^2)`
`=8x^3+y^3-8x^3+y^3`
`=2y^3`
`c)(a+b)^3-(a-b)^3-2b^3`
`=a^3+3a^2b+3ab^2+b^3-a^3+3a^2b-3ab^2+b^3-2b^3`
`=6a^2b`
`d)(a+b)^2-(a-b)^2`
`=a^2+2ab+b^2-a^2+2ab-b^2`
`=4ab`
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Chúc bạn học tốt!!!
`#Rùa~ ~ ~`
