# Math Help - Find a unit vector

1. ## Find a unit vector

Find a unit vector a which is horizontal and perpendicular to the vector b=4i -3j +7k.

2. Originally Posted by varunnayudu
Find a unit vector a which is horizontal and perpendicular to the vector b=4i -3j +7k.
how are you defining "horizontal" here? in the xy-plane?

if so, just make the z-coordinate zero. otherwise, we need the dot product of the vectors to be zero.

so the horizontal vector perpendicular to <a, b, c> is the vector <b, -a, 0>

so here, your vector would be, a = -3i - 4j

now find the unit vector in that direction