`4)27x^3-125=(3x-5)(9x^2+15x+25)`
`5)(2y-5)(4y^2+10y+25)=(2y)^3-5^3=8y^3-125`
`6)(3y-4)(9y^2+12y+16)=(3y)^3-4^3=27y^3-64`
`7)(x-3)^3+(2-x)^3=(x-3+2-x)[(x-3)^2-(x-3)(2-x)+(2-x)^2]=-(x^2-6x+9-2x+x^2+6-3x+4-4x+x)=-2x^2+14x-19`
`8)(x+y)^3-(x-y)^3=(x+y-x+y)[(x+y)^2+(x-y)(x+y)+(x-y)^2]=2y(x^2+2xy+y^2+x^2-y^2+x^2-2xy+y^2)=6x^2y+2y^3`