Let $\mathbf { r } ( t ) = \sin ( 3 t ) \mathbf { i } + \cos ( 3 t ) \mathbf { j } - t \mathbf { k }$

Multiple Choice

Let $\mathbf { r } ( t ) = \sin ( 3 t ) \mathbf { i } + \cos ( 3 t ) \mathbf { j } - t \mathbf { k }$ Then the unit normal vector $\mathbf { n } \left( \frac { \pi } { 6 } \right)$ is

A) $- \mathbf { i }$
B) k
C) j
D) i
E) $- \mathbf { j }$