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/sci/ - Science & Math

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4234232 No.4234232 [Reply] [Original]

Okay, so I have a coordinate system, and I want to calculate how many degrees there are from one point to another. both of the points can appear anywhere on the coordinate system

so, have x1, y1 and x2, y2 and need a formula to get how many degrees from the top the second point is relative to the first...

anyone know how to, been googling and reading about trigonometry but nothing seems to help

thanks

>> No.4234245

>>4234232
You can easily figure this shit out on your own.
Start and then ask questions.

>> No.4234251

>>4234245
Spent a good hour already and asked other people, have gotten nowhere.

>> No.4234256

lol sine law

>> No.4234258

>>4234256
shit no it's even dumber lol

>> No.4234266
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4234266

>>4234251
Fine, just because I am feeling generous.

For simplicity use vector notation, say:
Vector a = (x1, y1), vector b = (x2, y2).
http://en.wikipedia.org/wiki/Vector_%28mathematics_and_physics%29

Next, you need the concept of the "norm". If c is a vector c = (x3, y3), then |c| = sqrt(x3^2+y3^2)
http://en.wikipedia.org/wiki/Euclidean_norm

Lastly, you need the concept of the "dot product". Call the dot product of a and b, a.b
http://en.wikipedia.org/wiki/Dot_product

There are two equal ways to get the dot product of two vectors.
1) a.b = |a|*|b|*Cos[theta]
2) a.b = x1*x2 + y1*y2

Set 1) equal to 2) and solve for theta. This will be the angle between the vectors, a and b (what you are looking for).

Anyother questions?

>> No.4234267

Basic trig

>> No.4234269

Polar co-ordinates

Points defined by radius and angle

Your image will be wrong

>> No.4234270
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4234270

>>4234266

>> No.4234271

>>4234266
lol bullshit

>> No.4234273

>>4234266
Cool education bro

>> No.4234277
File: 30 KB, 555x644, 1298229612317.jpg [View same] [iqdb] [saucenao] [google]
4234277

>>4234266
theta =
ArcCos[
(x1*x2 + y1*y2)
/
( sqrt(x1^2+y1^2)*sqrt(x2^2+y2^2) )
]

\thread

>> No.4234278
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4234278

>>4234271

>> No.4234279

There is nothing good about this thread.

>> No.4234280

>>4234269
image is just to clarify

>> No.4234283

what is the metric of your coordinate system?

>> No.4234288
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4234288

>>4234279
>discuss basic freshman physics on a "science and math" board

>gets mad

>> No.4234291
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4234291

>>4234273

>> No.4234293

>>4234288
>implying this is even freshman level

>> No.4234295
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4234295

>>4234283
OP's metric is R^2.....DURRR

>> No.4234298

>>4234295
R^2 is not a metric

>> No.4234299
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4234299

>>4234293
They cover this shit in the remedial freshman physics classes (the kind the engineers have to take).

>> No.4234305
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4234305

>>4234298
Euclidean metric on R^2, if you want to get all anal about terminology.

>> No.4234307

>>4234299
I was implying it was at a lower level than freshman, which it is

>> No.4234309
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4234309

>>4234283
>can't infer the metric from the OP post

Get your head out of your ass.

>> No.4234311

>>4234305
in that case OPs problem is trivial

>> No.4234316
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4234316

>>4234307
>lower level than freshman

For physicists, chemists, and mathematicians, yes.

For engineers and biologists, no.

Different majors learn things at different times/different levels.

>> No.4234317 [DELETED] 

>>4234299
wow you are so sciencey

>> No.4234319

>>4234311
Trivial to a math or physics guy maybe. Not trivial to engineers.

>> No.4234332

Really? This stuff is not even hard high-school mathematics.

There is nothing good about this thread.

>> No.4234450

>discussion how easy the question is
>no right answer yet
Nice job there

>> No.4234488

>>4234450
a = ArcTan[(x1-c2)/(y1-y2-)]
woo, that was hard