Question

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

Answer 1

first expand the brackets \[p*p =p^2 and p*(-q) =-pq\] and for the other bracket \[-q*q =-q^2 and (-q )*(-p) =pq\]
therefore it is
\[p^2-pq-q^2+pq\]now cross out what ever you can cross out
at the end you are left with \[p^2-q^2\]

Answer 2

got it?