乜野係unit vector？

Unit vector is a vector whose magnitude is 1.
E.g. i , j , k
A vector b=xi+yj+zk
|b|=(x^2 + y^2 + z^2) sqrt.
The unit vector of b is that, the direction of b has not changed, but the magnitude.
^
b=(x^2+y^2+z^2)sqrt./|b|