Use the Dot Product to Find the Magnitude of U $\mathbf { u } = - 3 \mathbf { i } + 6 \mathbf { j }$

Multiple Choice

Use the dot product to find the magnitude of u if $\mathbf { u } = - 3 \mathbf { i } + 6 \mathbf { j }$

A) $\| \mathbf { u } \| = 18$
B) $\| \mathbf { u } \| =$ $6 \sqrt { 5 }$
C) $\| \mathbf { u } \| = 18$
D) ​ $\| \mathbf { u } \| =$ $3 \sqrt { 5 }$
E) $\| \mathbf { u } \| = 23$