Formula for angle between 2 lines
Hi ---
I can't figure out the yellow and red
parts of the solution to the problem below.
That picture at the bottom is mine. I drew it to try to help me but I am still
confused.
http://img833.imageshack.us/img833/6334/11201.jpg
Yellow: Where did they get $\displaystyle 180 - (\theta_2 - \theta_1)$ from? Why
do we care about this?
Red: If $\displaystyle \theta_2 < \theta_1$ why is $\displaystyle \alpha = 180 - (\theta_2 - \theta_1)$?
Thanks a lot ---
Re: Formula for angle between 2 lines
Yellow - You have it marked. Your $\displaystyle \theta_{1} - \theta_{2}$ is nicely labeled. What would you label the next angle - continuing anti-clockwise? It begins on your blue ray and ends with the portion of the red ray extended through the origin.
Red - This is just a second case. If you changed $\displaystyle \theta_{1}$ to 160º, would $\displaystyle \theta_{1} - \theta_{2}$ give an acute angle?
