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Q: Learn Sin, Cos, Tg ( No Answer,   1 Comment )
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 Subject: Learn Sin, Cos, Tg Category: Science > Math Asked by: jenkinsws-ga List Price: \$2.00 Posted: 21 Nov 2004 09:30 PST Expires: 21 Dec 2004 09:30 PST Question ID: 431904
 ```I can't remember any sin, cos, tg and cotg fomular! how can i know cosx+cosy eual what??? Pls help me learn by heart!```
 ```I have a HORRIBLE memory. I cannot memorize a formula to save my life. Yet, I am majoring in mathematics. I?m assuming you already know the sin= opposite/ hypotenuse type of rules and are looking for ways to memorize things like sin(x)^2+cos(x)^2=1. If you are looking for the first type of rule I suggest the age-old SOHCAHTOA rule: http://www.pen.k12.va.us/Div/Winchester/jhhs/math/facts/sohcahto.html. There are three ways to avoid having to force yourself to memorize formulii. The first (and my weapon of choice) is getting a good graphing calculator! The newer ones TI comes out with are capable of ?symbolic manipulation? (e.g. you say sin(x)/cos(x)*tan(x) and it says tan(x)^2). In my opinion math is about being able to solve problems, not to stuff easily forgotten rules in your head to pass tests. If you become calculator-literate you will be better suited to solving real-life problems in your future than those who were trained by their teachers not to use technology. In the very likely case that you aren?t allowed to use calculators to solve these problems (I should write a book on why teachers should never that do that) most of the trig rules stem from fairly simple algebra. If you?re strong at that you may be able to derive the formulas you need. By definition sin=opposite/hypotenuse, cos = adjacent/hypotenuse and tan = opposite/adjacent. Using algebra you can see that: sin/cos = (o/h)/(a/h) = o/a = tan If you replace every instance of sin with o/h, cos with a/h and tan with o/a you should be able to solve many of these problems without memorization. If you stick to this method I?m sure you?ll eventually pick up the rules...its sometimes easier to remember something once you understand the mechanics behind it. Once again, this approach will place you above those who simply remember the rules without knowing the math behind it. There are cases such as sin(r)^2+cos(r)^2=1 that algebra alone cant solve...for these you just need to remember the functions as used in a unit circle sin(r) is the y value, cos(r) is the x value. According to Pythagoras A^2+B^2=C^2...by the same logic (noting that on a unit circle C=1) sin^2+cos^2 = 1^2 = 1. There?s almost always a way to figure these rules out...you just have to be sneaky sometimes. My third idea is nothing new...but its sometimes the only way: practice. Don?t practice the rules per se, no flash cards needed. Practice in context, try to do a problem set from your textbook or online and keep track of how many you get right. If you?re in a jam you can always try using the algebraic approach above. You will most likely notice improvement after the first three or four times you go over it. If you need practice problems I?m sure you can ask a teacher, they always have out-dated textbooks lying around. I hope this helps. -Fractl```