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Understanding compund angle formulas 
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#1
Nov910, 02:08 PM

P: 467

1. The problem statement, all variables and given/known data
I can make intuitive sense out of cofunction identities but the compound angle results completely blows my mind. Is there a way to make sense of them without having to think about the proof everytime? Or should I just memorize them 2. Relevant equations 3. The attempt at a solution 


#2
Nov910, 10:27 PM

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In the case of the formulae such as [tex]sin(A+B)=sinAcosB+cosAsinB[/tex] it is much easier and definitely quicker to memorize than to reproduce in an exam. But I prefer to reproduce the cofunction identities than to memorize them because they are easy to do so, which you might as well.
I think it's just best to memorize these formulae. 


#3
Nov910, 10:36 PM

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I've been struggling with this on occasion too. Memorizing all of the identity formulas is too tough. There is a website, 'oakroadsystems' or something which gives advice on the Trigonometry identities. One idea that I had was to memorize (and also understand) a small number of very fundamental and easy ones, and learn to derive others from them. For the sum and difference of angles identities, just learn to derive a couple of them, and learn to derive many of the others using some algebraic steps. Use a graph picture to get started.



#4
Nov1010, 08:20 AM

P: 467

Understanding compund angle formulas
The proof for the addition/subtraction formula from my textbook seems completely arbitrary to me ~_~. I have found other proofs online that involve Euler's formula which I have not learned yet, as well as one that involves drawing two right angled triangles on top of each other. Which of the addition/subtraction formula proofs makes the most sense to you guys?



#5
Nov1010, 12:28 PM

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