/sci/ - Science & Math

I hit the wall again Bros.
for context
>2 months ago I was @ Med School, But I didn't liked to get shitted and pissed on, So I decided to drop out and go to Chem, so I have to Relearn All math and physics because of the UNI exam.

>Arithmetics Done
>Algebra 1 Done
>Algebra 2 Done

>Geometry Done/Trigonometry pending
Ok so this happened yesterday I started with Geometry, I was Happy measuring angles, drawing lines, doing goofy proofs and BORING algebra conversions between angle measures (Hexa,GMS, Radians with the π as a factor) BY HAND.

The problem came when the bitch from the Course I'm taking Jumped me with this "six circular functions" table and gave no explanation at all, and because I don't understand that I Can't move on.

Question 1:
I get the Sine and Cosine ones but The hell is up with the Domain of the Last 3, What is that Weird ass looking U symbol, WHAT DOES IT MEAN? Where does it derive?
I searched for U symbol in google but the only thing that comes up is the one used for unions of sets.

Question 2: How bad is it to do the Geo/Trigonometry exercises With a Calculator? it's just tedious to do all shit by hand, It isn't as fun as Algebra.

Resources to learn more of Trig are Appreciated.