How do you find a unit vector that is perpendicular to both the vector u = 0,2,1 and v = 1, -1, 1?

1 Answer
Sep 15, 2016

+-1/sqrt 14(3, 1, -2)±114(3,1,2), for opposite directions.

Explanation:

If vector u=(u_1, u_2, u_3) and v=(v_1, v_2, v_3)u=(u1,u2,u3)andv=(v1,v2,v3), then

vectors +-uXv=+-(u_2v_3-u_3v_2, u_3v_1-u_1v_3, u_1v_2-u_2v_1)±uXv=±(u2v3u3v2,u3v1u1v3,u1v2u2v1)

are perpendicular to both u and vuandv, in the opposite directions.

Here, u(0, 2, 1) and v=(1, -1, 1)u(0,2,1)andv=(1,1,1). So,

+-uXv±uXv

=+-((2)(1)-(1)(-1), (1)(1)-(0)((1), (0)(-1)-((2)(1))=±((2)(1)(1)(1),(1)(1)(0)((1),(0)(1)((2)(1))

=+-(3, 1, -2)=±(3,1,2).

For unit vectors,

divide by the modulus |(3, 1, -2)|=sqrt(3^2+(1)^2+(-2)^2)=sqrt 14,