Factorise:

 By suitably arranging the terms:

$x^{2}-x z+x y-y z=x^{2}+x y-x z-y z$

$=\left(x^{2}+x y\right)-(x z+y z)$

$=x(x+y)-z(x+y)$

$=(x+y)(x-z)$

$\therefore x^{2}-x z+x y-y z=(x+y)(x-z)$