Simplify p(p - q) - q(q - p).
p^2-pq-q^2+pq=p^2-q^2=(p+q)(p-q)=
p(p - q) - q(q - p). Multiply out.pp - pq - qq + qp. Note because of the minus before the bracket, the minus inside the bracket changes to +p² - pq -q² + pqp² - q² + pq - pqp² - q² + 0p² - q² = p² - q² I hope this helps.
