I understand that in order to find the angle between two lines, you can calculate the angle of inclination of each of the lines and take the difference between those two. However, I'm not sure exactly why the formula to calculate the angle of inclination is what it is. I'd love it if someone can provide a simple, intuitive explanation for that. Assume I know basic high school calculus? Thanks! Here's the formula I'm talking about:
$θ=\tan^{−1}m$
Look up the definition of $m$. It is the rise over the run. Then we have $\tan \theta = \frac m1$ by the definition of tangent. They are just inverting this.