`d)(1+2x)(1-2x)-x(x+2)(x-2)`
`=1-4x²-x(x²-4)`
`=1-4x²-x³+4x`
`=1+x²-5x²-x³+5x-x`
`=(x²+5x+1)-(x³+5x²+x)`
`=(x²+5x+1)-x(x²+5x+1)`
`=(1-x)(x²+5x+1)`
`e)x²+y²-x²y²+xy-x-y`
`=x²+y²-x²y²+xy+xy-xy-x-y+x²y-x²y+xy²-xy²`
`=(x²y+x²+xy)+(xy²+xy+y²)-(x²y²+x²y+xy²)-(xy+x+y)`
`=x(xy+x+y)+y(xy+x+y)-xy(xy+x+y)-(xy+x+y)`
`=(x+y-xy-1)(xy+x+y)`
`=[(x-1)-(xy-y)](xy+x+y)`
`=[(x-1)-y(x-1)](xy+x+y)`
`=(x-1)(1-y)(xy+x+y)`
`f)x^4+2x³-4x-4`
`=x^4+2x³+2x²-2x²-4x-4`
`=(x^4+2x³+2x²)-(2x²+4x+4)`
`=x²(x²+2x+2)-2(x²+2x+2)`
`=(x²-2)(x²+2x+2)`
`g)x³-7x-6`
`=x³-6x-x-6`
`=(x³-x)-(6x+6)`
`=x(x²-1)-6(x+1)`
`=x(x+1)(x-1)-6(x+1)`
`=(x+1)[x(x-1)-6]`
`=(x+1)(x²-x-6)`
`=(x+1)(x²-3x+2x-6)`
`=(x+1)[x(x-3)+2(x-3)]`
`=(x+1)(x+2)(x-3)`
`h)x²+2xy+y²-x-y`
`=(x²+2xy+y²)-(x+y)`
`=(x+y)²-(x+y)`
`=(x+y)(x+y-1)`
`i)5x²-10xy+5y²-20z²`
`=5(x²-2xy+y²-4z²)`
`=5[(x²-2xy+y²)-4z²]`
`=5[(x-y)²-(2z)²]`
`=5(x-y+2z)(x-y-2z)`
`k)x²-5x-5y-y²`
`=(x²-y²)-(5x+5y)`
`=(x+y)(x-y)-5(x+y)`
`=(x+y)(x-y-5)`
`l)x²-4x-5`
`=x²-5x+x-5`
`=(x²-5x)+(x-5)`
`=x(x-5)+(x-5)`
`=(x-5)(x+1)`
`m)(x²+1)^2-4x²`
`=(x²+1)^2-(2x)^2`
`=(x²+2x+1)(x²-2x+1)`
`=(x+1)²(x-1)²`
`n)3x²-6xy+3y²-12z²`
`=3(x²-2xy+y²-4z²)`
`=3[(x²-2xy+y²)-4z²]`
`=3[(x-y)²-(2z)²]`
`=3(x-y+2z)(x-y-2z)`
