How to know cos sin tan

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hello everyone! I wanna know how to verify cos sin tan
I always feel confused when i am doing the physics exercises.
are we always use cos when it is x-axis and use sin when it is y-axis??
I feel so confused.
 

tony873004

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It's almost always cos for x and sin for y.
Snell's Law is an exception. You measure your angles off the normal rather than the x-axis. In either case, its pure soh cah toh. Don't memorize it. Like jedishrfu says, "just draw it out".
 

SteamKing

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It's almost always cos for x and sin for y.
Except when it isn't. That's why you should memorize the definitions of sine, cosine, and tangent using a typical right triangle:

trig_defs_1.gif
 

rcgldr

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The old way "sohcahtoa" == sin => opposite over hypotenuse, cos = adjacent over hypotenuse, tan = opposite over adjacent.
 

davenn

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haven't heard that one before
 

sophiecentaur

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hello everyone! I wanna know how to verify cos sin tan
I always feel confused when i am doing the physics exercises.
are we always use cos when it is x-axis and use sin when it is y-axis??
I feel so confused.
Since I was at school, I have been using a good 'cheat' method to check whether I should be using sin or cos. It avoids the 'x-axis / y-axis' question. What you do is to imagine that the angle in question is nearly zero (just imagine lowering the slope or altering the direction of the string etc.). Then decide whether the effect of the force would be to be small and increasing, as you increase the angle (in which case you choose sine) OR whether the effect of the force will be big and decreasing as you increase the angle (in which case, choose cosine). Try it for a simple example where you already know the answer and you will see what I mean. I think that advice helped a number of my students, who were confused in the same way.
Of course, there's no real substitute for drawing the proper vector diagram and really sticking to the rules you've been taught but the above method should give you confidence. There is also the problem of getting the right angled triangle the right way round (with the 90° in the right place). Just practice, is all I can tell you.
 

sophiecentaur

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MR Worthington taught us: Some Old Hulks Carry A Huge Tub Of Ale. Could I ever forget that?
 

sophiecentaur

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MR Worthington taught us: Some Old Hulks Carry A Huge Tub Of Ale. Could I ever forget that?
[Edit: Sorry about the repeat. My domestic wifi plays up sometimes.]
 
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I have very poor memory, I remember concepts / connection... so what worked for me was Remembering Sin (0) = 0 and Tan(0)=0

So Knowing Sin 0 = 0 means it must include the Opp in the Numerator ( as the angle goes to 0 - the Opp does, and you know nothing about the Adj and Hyp) - same for Tan (0) = Sin /Cos = again Opposite must be in the numerator, and thus Sin must be in the Numerator.. I know this is weird but there is no other solution. For example if Tan (0) = Cos/ Sin - and Sin(0) ... this would be undefined, etc...

This basic fact helped me test into Calc 1 - not having taken any Trig in HS.
 
199
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We learned "Oscar Had A Heap Of Apples".
But then you have to remember that the order is sin, cos, tan.
 

davenn

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It's been around as long as I can remember.
Hi Mark

an American thing maybe ?

Some Old Hulks Carry A Huge Tub Of Ale.
like that one too :smile:


with this topic and other basic stuff I have seen on PF over the years
I find it a bit bewildering thinking back and realising all these things I was never taught at school :frown:

Dave
 
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Some Old Hags Can't Hide There Old Age.


That's how my math teacher taught it, schools were less than PC then.
 
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At school I was taught "Peter has been here playing billiards"
 

NascentOxygen

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Some Old Hags Can't Hide There Old Age.


That's how my math teacher taught it, schools were less than PC then.
You'll ALWAYS remember that ditty?
 

epenguin

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How do any of them help? Mystified.
 
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How do any of them help? Mystified.
Really?
They are mnemonic devices
SOH -- sin = opp/hyp
CAH -- cos = adj/hyp
TOA -- tan = opp/adj
Some Old Hags Can't Hide There Their Old Age.
Some Old Hags - same as above
Can't Hide - cosine, with 'c' for cosine and 'a' for adjacent, Hags for hypotenuse
Their Old Age - same as above
 

NascentOxygen

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Really?
They are mnemonic devices
SOH -- sin = opp/hyp
CAH -- cos = adj/hyp
TOA -- tan = opp/adj

Some Old Hags - same as above
Can't Hide - cosine, with 'c' for cosine and 'a' for adjacent, Hags for hypotenuse
Their Old Age - same as above
My hint about the missing 'A' word was maybe too subtle. :sorry:

Some Old Hags Can't Always Hide Their Old Age
 

Mark Harder

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SOH CAH TOA is definitely an American thing...

(http://www.slideshare.net/shmurray/sohcahtoa-indian-story)

SOHCAHTOA is a Native American.
Yeah, that's how I first heard it "Chief Soh Cah Toa". I guess somebody thought it sounded native American. Maybe there was such a person. But I I ignore the whole Indian thing. Just plain old soh cah toa works for me. As for x and y, forget that description. It's really a special case and it's misleading. Trigonometric functions relate to angles in a triangle or circular rotations of a vector about a point, and so forth. They're co-ordinate free, and that includes circular coordinates.
 

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