# Math Help - Angle between a vector and the y-axis

1. ## Angle between a vector and the y-axis

Determine the angle that the vector a = (12, -3, 4) makes with the y-axis.

Would I still use the dot product? I'm confused on how I would go about do it as I'm not too familiar with three dimensional vectors. All help appreciated!

2. Originally Posted by IanCarney
Determine the angle that the vector a = (12, -3, 4) makes with the y-axis.
$\mathbf{j}=<0,1,0>$.
Find $\arccos \left( {\frac{{a \cdot j}}{{\left\| a \right\|}}} \right)$

3. Originally Posted by Plato
$\mathbf{j}=<0,1,0>$.
Find $\arccos \left( {\frac{{a \cdot j}}{{\left\| a \right\|}}} \right)$
Okay I think I got it. I was doing something wrong before so I got a different answer than the book. Thanks again for all your help!