Question

Simplify p(p - q) - q(q - p).

Answer 1

P^2-pq-q^2+pq=
p^2-q^2=
(p+q)(p-q)=

Answer 2

P(p - q) - q(q - p).    Multiply out.

p*p - p*q - q*q + q*p.         

Note because of the minus before the bracket, the minus inside the bracket changes to +

p² - pq -q² + pq

p² - q² + pq - pq

p² - q² + 0

p² - q²

= p² - q²

I hope this helps.