June 17th, 2015, 09:44 AM  #1 
Newbie Joined: Jun 2015 From: St. Louis, Missouri Posts: 3 Thanks: 0  What and When
I am really having a hard time understanding which formula to use for which type of problem or when to use a certain formula. I see when working problems that if I work it too long to get the answer, I should not have. And if I don't work a problem long enough, I should have kept on working it. ugh what to do, what to do? Also there are soooooo many formulas, and can not use notes, so how does a person remember all of those formulas and when to use them? WHO AND WHY DID THEY COME UP WITH TRIGONOMETRY?! 
June 17th, 2015, 10:52 AM  #2 
Math Team Joined: Jan 2015 From: Alabama Posts: 3,264 Thanks: 902 
It sounds to me like you are memorizing formulas rather than understanding exactly what the formulas say and what the various symbols in them mean learn the concepts, not the formulas.

June 17th, 2015, 11:28 AM  #3 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,654 Thanks: 2632 Math Focus: Mainly analysis and algebra 
When working a problem, you should plan your approach. What steps do you need to take to get your answer? Perhaps you would decide that, if you can find the length AB, then you can determine the angle $\theta$ that you need. You make these plans based on the formulae that you know. A formula is generally useful if (and often only if) you already know all but one of the variables it contains. It then allows you to find the other. On occasion you might find that you have two formulae and that you know all variables for each except for the same pair. In this case you can create a pair of simultaneous equations for the two variables. Solving problems usually involves one or more uses of formulas as given above. Solving problems is not a competition to get the result in the quickest way possible, it is only about getting the correct result. Sometimes, after we have solved a problem we may see a quicker or "better" way to do it. That's fine, it doesn't make the first answer wrong. Last edited by v8archie; June 17th, 2015 at 11:30 AM. 
June 17th, 2015, 07:34 PM  #4 
Senior Member Joined: Nov 2010 From: Indonesia Posts: 2,001 Thanks: 132 Math Focus: Trigonometry 
You only need to memorize the basic ones, because all the others are just derived from tha basic formulae. Here I give you an example in the discussion from my old thread: Integral of Trigonometry 