How to draw construction lines at odd angles?

[SilverAstronauts]

Apologies for my seemingly beginner question. But I'm currently trying to design a home theater room and I'd like to design the room to be capable of adopting dolby's 7.1 surround system speaker placement guidelines according to the website below.

 

https://www.dolby.com/us/en/guide/surround-sound-speaker-setup/7-1-setup.html

 

This guide provides optimal angles at which each set of speakers are to be placed from the intended listener/viewer. So I began to simply use the line tool to draw "cones" of possible speaker placements. However, the lines are limited to the snap angles of the document properties. I believe those are every 15 degrees. I don't... actually want to change the snap angles. I WANT to be able to select two lines and define the angle between those two lines. Just like in most CAD programs. 

 

I suppose I could draw triangles and use trigonometry. But... I mean, that seems a bit overboard. I guess it wouldn't be too hard to do so. But there must be an easier way.

 

EDIT: In attempting to use Trig, I found you can set the angle if you double click on a line drawing of 2 lines. However, it is quite... ungainly.

 

EDIT2: AANNNDD I just found the angular dimension tool.

[rgardner]

You can also click the line and open the dbx and set the angle of the line(s).