sin2A + cos2A
In Geometry, you learn about triangles. In Trigonometry you learn even more about triangles.
conclusion
It depends. Between 9th to 12th.
Learn the subject!
The disadvantage of trigonometry is that it requires an intellectual effort to learn it. It is much easier to eat pizza, than it is to learn trigonometry. Put down that textbook and order a pizza. Yum!
Trigonometry isn't required to learn calculus, but it does help you to understand some of the concepts. Geometry, however, is usually required before taking a course in trigonometry.
SOH KAH TOA
If they put their mind to it, it is not difficult.
YES! If you can't do algebra, you won't last ten seconds in trigonometry. It basically is algebra, just using equations within equations.
Trigonometry is engineering math, but If you are going to study something in physics, or science, (basically this is "applied science"), you will need lots of calculus. calculus appears a lot in "Stargate".
Pay attention in class. That is the simplest way.
Math gets much better once you get past trigonometry into Calculus. You learn trig to help with many things later in life. (Believe me you will use it). Calculus can be used to describe ANYTHING, and is so powerful that you will be amazed when you learn it. Things that you thought you could never understand because they were too difficult suddenly you can. So just keep plugging away at trigonometry and I promise it will get better and they will be the most important things you learn in school.