Factorize each of the following expressions:
(1)`q r-p r+q s-p s`
(2) `p^2q-p r^2-p q+r^2`
(3)`1+x+x y+x^2y`
(4) `a x+a y-b x-b y`

Explanation

Given:

(1)`q r-p r+q s-p s`

`=>r(q -p )+s(q -p )`

`=>(r+s)(q -p )`

(2) `p^2q-p r^2-p q+r^2`

`=> p^2q-p q-pr^2+r^2`

`=> pq(p-1)-r^2(p-1)`

`=> (pq-r^2)(p-1)`

...