\(\eqalign{
&a)\; {x^2} - xy + x - y \cr
& = ({x^2} - xy) + \left( {x - y} \right) \cr
& = x\left( {x - y} \right) + \left( {x - y} \right) \cr
& = \left( {x - y} \right)\left( {x + 1} \right) \cr} \)
\(\eqalign{
& b)\;xz + yz{\rm{ }} - 5\left( {x + y} \right) \cr
& = \left( {xz + yz{\rm{ }}} \right) - 5\left( {x + y} \right) \cr
& = z\left( {x + y} \right) - 5\left( {x + y} \right) \cr
& = \left( {x + y} \right)\left( {z - 5} \right) \cr} \)
\(\eqalign{
& c)\,\,3{x^2} - 3xy - 5x + 5y \cr
& = (3{x^2} - 3xy) + \left( { - 5x + 5y} \right) \cr
& = 3x\left( {x - y} \right) - 5\left( {x - y} \right) \cr
& = \left( {x - y} \right)\left( {3x - 5} \right) \cr} \)
