Let the angle $\displaystyle \theta$ be the angle that the vector $\displaystyle \vec{A}$ makes with the +x-axis, measured counterclockwise from that axis. Find the angle $\displaystyle \theta$ for a vector that has the following components.

First one is $\displaystyle A_{x}=$1.30 m, $\displaystyle A_{y}= $-3.40.

I've read the section, but it's not helping. It lists a couple of equations such as $\displaystyle \frac{A_{x}}{A}=\cos\theta$, but I don't see how that helps me.