Question

factorize p×p×q-p×r×r-p×q+r×r

Answer 1

(p×p×q)-(p×r×r)-(p×q)+(r×r)
1. 2. 3. 4.

take pq common from 1 and 3
then take -r×r common from 2 and 4.

expression turn into:
p×q(p-1)-r×r(p-1)

then take p-1 common from above expression.
the result will be:
(p-1)-(p×q-r×r)