Question 273311
p^2 - q^2 = (p+q) * (p-q)


(p+q) * (p-q) = p*(p-q) + q*(p-q) which equals:


p^2 - pq + qp - q^2 


since pq is the same as qp, this expression becomes:


p^2 - pq + pq - q^2


The -pq and the +pq cancel out and you are left with:


p^2 - q^2