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 05-21-07, 02:45 PM #1 ManBearPig 1/2 man,1/2 bear,1/2 pig Thread Starter     Join Date: May 2004 Location: . Bikes: . Posts: 1,122 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Math Majors -- simplify this If you can, please simplify this expression: SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X)) The expression in the COS( ) looks familiar to me, but it has been 10 years since I finished my engineering degree. Thanks! __________________ ...
 05-21-07, 02:47 PM #2 Taerom Hazardous     Join Date: Jun 2005 Location: Quarantine Bikes: 2005 Trek Liquid 55, 2009 Haro Mary SS Posts: 727 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) 42
05-21-07, 02:50 PM   #3
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Quote:
 Originally Posted by Towlie If you can, please simplify this expression: SATAN The expression in the COS( ) looks familiar to me, but it has been 10 years since I finished my engineering degree. Thanks!
I removed all the unnecesasry stuff and got the answer to your math problem
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 05-21-07, 02:51 PM #4 ManBearPig 1/2 man,1/2 bear,1/2 pig Thread Starter     Join Date: May 2004 Location: . Bikes: . Posts: 1,122 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Please, express the answer in terms of X and Y only; no supernatural deities. __________________ ...
 05-21-07, 02:52 PM #5 x136  phony collective progress     Join Date: Sep 2006 Location: San Hoosey Bikes: http://velospace.org/user/36663 Posts: 2,981 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Who is this Y? Is she hot? __________________
05-21-07, 02:58 PM   #6
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Quote:
 Originally Posted by Taerom 42
+1

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 Originally Posted by coffeecake - it's pretty well established that Hitler was an *******.

 05-21-07, 03:09 PM #7 ManBearPig 1/2 man,1/2 bear,1/2 pig Thread Starter     Join Date: May 2004 Location: . Bikes: . Posts: 1,122 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) This ain't homework. The question is directed to math majors, not math phobics. This is not an advanced problem in the grand scheme of things; I am simply rusty on my trig and algebra. __________________ ...
05-21-07, 03:13 PM   #8
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 Originally Posted by Taerom 42
what else ..... and thanks for the fish.

05-21-07, 03:16 PM   #9
KingTermite
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Quote:
 Originally Posted by Towlie This ain't homework. The question is directed to math majors, not math phobics. This is not an advanced problem in the grand scheme of things; I am simply rusty on my trig and algebra.
No it's not advanced....never said it was. I'm not a math phobic by ANY stretch of the definition (I have a bachelors and masters degree in computer engineering...methinks I've taken some math courses).....I still think it looks like you are trying to get help with a homework problem.
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 Originally Posted by coffeecake - it's pretty well established that Hitler was an *******.

 05-21-07, 03:31 PM #10 ManBearPig 1/2 man,1/2 bear,1/2 pig Thread Starter     Join Date: May 2004 Location: . Bikes: . Posts: 1,122 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) I am 33 yrs old; I am not doing homework; I am a BSME (UT Austin, May, 1997)....I derived this expression trigonometrically on a project I am working on, and I don't know/remember how to simplify it. I don't remember all the trigonometric identities because I haven't worked with them for a long while, e.g. http://www.sosmath.com/trig/Trig5/trig5/trig5.html __________________ ...
05-21-07, 03:40 PM   #11
CdCf
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Quote:
Originally Posted by KingTermite
Quote:
 Originally Posted by Taerom 42
+1
43!

I don't think I could simplify it further myself, but I'm not very good at math anyway. Why can't you use it as it is?

 05-21-07, 03:47 PM #12 ManBearPig 1/2 man,1/2 bear,1/2 pig Thread Starter     Join Date: May 2004 Location: . Bikes: . Posts: 1,122 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) I guess I could - but if there were a generally known trigonometric identity in the field, it might look dumb for me to express it in an unnecessarily complicated fashion (e.g., to make something up, suppose everythinig in the parantheses could be replaced by cos(x/y) or something simple like that). __________________ ...
05-21-07, 03:49 PM   #13
KingTermite
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Quote:
 Originally Posted by Towlie I am 33 yrs old; I am not doing homework; I am a BSME (UT Austin, May, 1997)....I derived this expression trigonometrically on a project I am working on, and I don't know/remember how to simplify it. I don't remember all the trigonometric identities because I haven't worked with them for a long while, e.g. http://www.sosmath.com/trig/Trig5/trig5/trig5.html
I'm only calling it how it looked. See it from "our" point of view. Too many kids come on here and try to get help with their homework....quite often. It would be good for you to explain your situation so we don't think (like I did) that you are a 16 year old looking for homework help. I'm sorry if I offended....but that sure is how it looked.
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 Originally Posted by coffeecake - it's pretty well established that Hitler was an *******.

05-21-07, 03:56 PM   #14
mtnbk3000
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 Originally Posted by scrapmetal what else ..... and thanks for the fish.
whats up with people and hitchikers guide to the galaxy

 05-21-07, 04:10 PM #15 lyeinyoureye Senior Citizen     Join Date: Feb 2005 Location: no Bikes: yes Posts: 1,347 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) If you actually have a BSME, then you should now how to do this as a matter of course imo. Nothing scares me more than engineering majors that don't know their shiz, because it's an applied skill. Unlike something like english, or even pure math, where screw ups can result in poor marks or scathing peer reviews, but shiz can't really go that bad from a practical perspective. Heh, ManBearPig.
 05-21-07, 04:43 PM #16 EJ123 djentleman     Join Date: Aug 2005 Bikes: Posts: 3,370 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 5 Post(s) Answers.yahoo.com
05-21-07, 04:44 PM   #17
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Quote:
 Originally Posted by Towlie If you can, please simplify this expression: SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X)) The expression in the COS( ) looks familiar to me, but it has been 10 years since I finished my engineering degree. Thanks!
(X±Y)1/2*COS[45-ATANG(Y/X)]
=(X±Y)(X±Y)(COS)(45-X/Y)?

I think that's how it would factor out.
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 05-22-07, 03:52 AM #18 j-dowsett Senior Member   Join Date: May 2005 Location: Salisbury, UK Bikes: Decathlon R 7.4 Posts: 55 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) It'll give you the length of the vector from the origin to (x,y) projected onto the line x = y. Though that might be how you derived it in the first place! Simplifying it? Hmm, thinking dot product could be useful, (also thinking as typing so bear with me). (x,y).(0.707, 0.707) = 0.707x + 0.707y excel confirms. where 0.707 is actually meant to be 1/sqrt(2) Possible complications outside of the range 0-90 degrees due to the atan not being unique. Can't be bothered to think that hard though. Apologies to those arguing the poster should have solved it themselves. But I needed some mental exercise due to having been laid up in hospital for four weeks avoiding my maths lectures. edit: Just managed it properly too. let sqrt() denote SQRT(X^2 + Y^2) for easy writing. SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X)) =sqrt() * [ cos(45)*cos(atan(y/x) + sin(45)*sin(atan(y/x)] =sqrt() * [ 0.707 * x / sqrt() + 0.707 * y / sqrt() ] =0.707 * (x + y) Last edited by j-dowsett; 05-22-07 at 07:01 AM.
05-24-07, 08:03 PM   #19
ManBearPig
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Quote:
 Originally Posted by j-dowsett It'll give you the length of the vector from the origin to (x,y) projected onto the line x = y. Though that might be how you derived it in the first place! Simplifying it? Hmm, thinking dot product could be useful, (also thinking as typing so bear with me). (x,y).(0.707, 0.707) = 0.707x + 0.707y excel confirms. where 0.707 is actually meant to be 1/sqrt(2) Possible complications outside of the range 0-90 degrees due to the atan not being unique. Can't be bothered to think that hard though. Apologies to those arguing the poster should have solved it themselves. But I needed some mental exercise due to having been laid up in hospital for four weeks avoiding my maths lectures. edit: Just managed it properly too. let sqrt() denote SQRT(X^2 + Y^2) for easy writing. SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X)) =sqrt() * [ cos(45)*cos(atan(y/x) + sin(45)*sin(atan(y/x)] =sqrt() * [ 0.707 * x / sqrt() + 0.707 * y / sqrt() ] =0.707 * (x + y)

Thanks, man. I actually logged in because I found the answer on my own and wanted to post it. The result I found was (X+Y) / SQRT(2). Soooooo simple. I found the answer numerically, plugging in numbers into a table and playing around with them.
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05-25-07, 05:06 AM   #20
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ouch. math. I mean, I love it and all but I've done my time. University flashbacks
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05-25-07, 09:04 AM   #21
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Quote:
 Originally Posted by Towlie If you can, please simplify this expression: SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X)) The expression in the COS( ) looks familiar to me, but it has been 10 years since I finished my engineering degree. Thanks!
Where are you trying to get to? The Atan will give you and angle that you then subtract from 45° get the Cos of that ...
So as long as you know x&y things should be ok. Or are you trying to use this to determine x&y?

Joe

 05-25-07, 07:43 PM #22 junkyard Fourth Degree Legend     Join Date: Jun 2005 Location: American Gardens Building Bikes: 2005 Kona Cinder Cone & 2010 Cannondale SuperSix Posts: 3,826 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) 42 4*2 8
05-25-07, 08:07 PM   #23
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 Originally Posted by joeprim Where are you trying to get to? The Atan will give you and angle that you then subtract from 45° get the Cos of that ... So as long as you know x&y things should be ok. Or are you trying to use this to determine x&y? Joe
I have no idea, I got lost at that point!
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