The Value of a That Makes $\mathbf { v } = 6 \mathbf { i } - 4 \mathbf { j } + \mathbf { k }$

Multiple Choice

The value of a that makes $\mathbf { v } = 6 \mathbf { i } - 4 \mathbf { j } + \mathbf { k }$ and $\mathbf { w } = a \mathbf { i } - \mathbf { j } - \mathbf { k }$ orthogonal is

A) -1
B) $- \frac { 1 } { 2 }$
C) -2
D) $\frac { 1 } { 2 }$
E) 2