Find the Principal Unit Normal Vector N for the Curve $$\mathbf { r } ( t ) = ( 10 + t ) \mathbf { i } + ( 9 + \ln ( \cos t ) ) \mathbf { k } , - \pi / 2 < t < \pi / 2$$

Multiple Choice

Find the principal unit normal vector N for the curve r(t) .
- $$\mathbf { r } ( t ) = ( 10 + t ) \mathbf { i } + ( 9 + \ln ( \cos t ) ) \mathbf { k } , - \pi / 2 < t < \pi / 2$$

A) N = (-cos t) i - (ln(cos t) ) k
B) N = (cos t) i + (sin t) k
C) N = (-sin t) i - (cos t) k
D) N = (-cos t) i - (tan t) k