`g)``(x+y+z).(x-y-z)`

`=x^2-(y+z)^2`

`=x^2-(y^2+2yz+z^2)`

`=x^2-y^2-2yz-z^2`

`h)``(x-y+z).(x+y+z)`

`=(x+z)^2-y^2`

`=x^2+2xz+z^2-y^2`