The Speed of a Particle Moving Along the Curve $\mathbf { r } ( t ) = \cos ( 2 t ) \mathbf { i } + \sin ( 2 t ) \mathbf { j } + 3 t \mathbf { k }$

Multiple Choice

The speed of a particle moving along the curve $\mathbf { r } ( t ) = \cos ( 2 t ) \mathbf { i } + \sin ( 2 t ) \mathbf { j } + 3 t \mathbf { k }$ is

A) $\sqrt { 8 t ^ { 2 } - 1 }$
B) $\sqrt { 13 }$
C) $\sqrt { 8 t ^ { 2 } + 1 }$
D) $\sqrt { 5 }$
E) $\sqrt { 7}$