Đáp án+Giải thích các bước giải:
`11)5y^3-10xy^2+5x^2y-20y`
`=5y(y^2-2xy+x^2-4)`
`=5y[(x-y)^2-4]`
`=5y(x-y-2)(x-y+2)`
`12)x^2+2xy+y^2-xz-yz`
`=(x+y)^2-z(x+y)`
`=(x+y)(x+y-z)`
`13)9x^2+y^2+6xy`
`=(3x+y)^2`
`14)8-12x+6x^2-x^3`
`=2^3-3.2^{2}.x+3.2.x^2-x^3`
`=(2-x)^3`
`15)125x^3-75x^2+15x-1`
`=(5x)^3-3.(5x)^2+3.5x-1`
`=(5x-1)^3`
`16)x^2-xz-9y^2+3yz`
`=x^2-9y^2-xz+3yz`
`=(x-3y)(x+3y)-z(x-3y)`
`=(x-3y)(x+3y-z)`
`17)x^3-x^2-5x+125`
`=x^3+125-x^2-5x`
`=(x+5)(x^2-5x+25)-x(x+5)`
`=(x+5)(x^2-6x+25)`
`18)x^3+2x^2-6x-27`
`=x^3-27+2x^2-6x`
`=(x-3)(x^2+3x+9)+2x(x-3)`
`=(x-3)(x^2+5x+9)`
`19)3a^2-6ab+3b^2-12c^2`
`=3(a^2-2ab+b^2-4c^2)`
`=3[(a-b)^2-(2c)^2]`
`=3(a-b-2c)(a-b+2c)`
`20)a^4+4b^4`
`=(a^2)^2+2.a^{2}.(2b^2)^2+(2b)^2-4a^2b^2`
`=(a^2+2b^2)^2-(2ab)^2`
`=(a^2-2ab+2b^2)(a^2+2ab+2b^2)`
