Question

Determine the cross product b*a a=2i+2j-5k b=6i-j+2k

Answer 1

Recall the definition of the cross product:

i x i = j x j = k x k = 0

i x j = k

j x k = i

k x i = j

The cross product is antisymmetric, or anticommutative, meaning that for any  vectors u and v, we have u x v = - (v x u).

It's also distributive, so for any vectors u, v, and w, we have (u + v) x w = (u x w) + (v x w).

Taking all of these properties together, we get

b x a = (6i - j + 2k) x (2i + 2j - 5k)

b x a = 12 (i x i) - 2 (j x i) + 4 (k x i)

............. + 12 (i x j) - 2 (j x j) + 4 (k x j)

............. - 30 (i x k) + 5 (j x k) - 10 (k x k)

b x a = 1 (j x k) + 34 (k x i) + 14 (i x j)

b x a = i + 34j + 14k