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Theorem 2: Algebraic Rules for Inner Products

Here is a list of algebraic rules for inner products. All the rules are easy to prove in either two or three dimensions.

THEOREM 2

(Algebraic Rules for Inner Products)

(i)     A · i = a1, A · j = a2, A · k = a3.

(ii)     A · 0 = 0 · A = 0.

(iii)    A · B = B · A (Commutative Law).

(iv)     A · (B + C) = A · B + A · C (Distributive Law).

(v)    (tA) · B = t(A · B) (Associative Law).

(vi)    A · A = |A|2.

PROOF

Rule (vi) is proved as follows in three dimensions.

A · A = a1a1 + a2a2 + a3a3 = a12 + a22 + a32 = |A|2.

Inner products are useful in the study of perpendicular and parallel vectors.


Last Update: 2006-11-06