Đáp án + Giải thích các bước giải:
`3.`
`a)` `x^2-6xy+9y^2`
`=x^2-2*x*3y+(3y)^2`
`=(x-3y)^2`
`b)` `x^3+6x^2y+12xy^2+8y^3`
`=x^3+3*x^2*2y+3*x*(2y)^2+(2y)^3`
`=(x+2y)^3`
`c)` `x^3-64`
`=x^3-4^3`
`=(x-4)(x^2+4x+4^2)`
`=(x-4)(x^2+4x+16)`
`d)` `125x^3+y^6`
`=(5x)^3+(y^2)^3`
`=(5x+y^2)[(5x)^2-5xy^2+(y^2)^2]`
`=(5x+y^2)(25x^2-5xy^2+y^4)`
`e)` `0,125(a+1)^3-1`
`=1/8(a+1)^3-1`
`=[1/2(a+1)]^3-1^3`
`=(1/2a+1/2)^3-1^3`
`=(1/2a+1/2-1)[(1/2a+1/2)^2+(1/2a+1/2)*1+1^2]`
`=(1/2a-1/2)[(1/2a)^2+2*1/2a*1/2+(1/2)^2+1/2a+1/2+1]`
`=(1/2a-1/2)(1/4a^2+1/2a+1/4+1/2a+1/2+1)`
`=(1/2a-1/2)(1/4a^2+a+7/4)`.
