1,
a,
`3xy^2-12xy+12x`
`=3x(y^2-4y+4)`
`=3x(y-2)^2`
b,
`x^2+2xy+y^2-xz-yz`
`=(x+y)^2-z(x+y)`
`=(x+y)(x+y-z)`
c,
`4x^4-x^3+3x^2-x`
`=x(4x^3-x^2+3x-1)`
d,
`x^4+2x^3+x^2-y^2`
`=(x^2+x)^2-y^2`
`=(x^2+x-y)(x^2+x+y)`
e,
`2x-2y-x^2+2xy-y^2`
`=2(x-y)-(x-y)^2`
`=(x-y)(2-x+y)`
g,
`4x^4+y^4`
`=4x^4+4x^2y^2+y^4-4x^2y^2`
`=(2x^2+y^2)^2-4x^2y^2`
`=(2x^2+y^2-2xy)(2x^2+y^2+2xy)`
h,
`2xy-x^2-y^2+16`
`=16-(x^2-2xy+y^2)`
`=16-(x-y)^2`
`=(4+x-y)(4-x+y)`
