Asked by Jess

Let a, b, c and d be vectors.
(i) Show that
(a - b) * (a + b) = a^2 - b^2
Answered by Steve
(a-b)•(a+b) = a•a - a•b + a•b - b•b
= |a|<sup>2</sup> - |b|<sup>2</sup>