$\\$
`d,`
`x^2 +4x-y^2+4`
`= (x^2 + 2 . x . 2 +2^2) - y^2`
`= (x+2)^2 -y^2`
`= (x+2-y) (x+2+y)`
`= (x-y+2)(x+y+2)`
$\\$
`e,`
`3x^2 + 6xy +3y^2 -3z^2`
`= 3 (x^2 + 2xy + y^2 - z^2)`
`= 3 [(x+y)^2 - z^2]`
`= 3 (x+y-z)(x+y+z)`
$\\$
`f,`
`x^2 - 2xy + y^2 - z^2 + 2zt - t^2`
`= (x^2 - 2xy+y^2) - (z^2 - 2zt + t^2)`
`= (x-y)^2 - (z-t)^2`
`= (x-y-z+t) (x-y+z-t)`