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 12-14-2011, 05:26 PM #251 Unaffiliated Registered User     Join Date: Aug 2010 Location: Richmond, B.C. Country: Posts: 10,284 vCash: 500 Just finished my Partial Differential Equations exam! With 40 minutes left I had only done 3/5 questions -- the others had me confused. Then I suddenly realized what I was supposed to do on both, and flew through them. Should probably end up with 90ish on the exam . I went into the exam with 98% and 96% on my two midterms and 90+% on homework. SO AMPED. Math talk below: The questions I couldn't figure out were: a) heat equation (ut = uxx) with time-dependent source term. had to use eigen-expansion of the heat equation part [u(x,t)] and the source term [s(x,t]. Here s(x,t) = t For some reason I panicked when I had to expand s(x,t) = Σsn(t)cos(λx) and erased everything and tried to find a v(x,t) to get rid of the source term in the HE. Then later on I realized that I was an idiot and that t = Σsn(t)cos(λx) works fine. I didn't get all the way to the final solution because there's a HUGE amount of trivial math to do, but I wrote the rest of the steps of the solution from where I was in English, which should get me big part marks. b) Polar Laplacian urr + (1/r)ur + (1/r^2)uθθ = 0 I couldn't figure out the solution to R-problem in the separation of variables. Apparently it's something to do with the euler equation. Anyway, I just inferred the R-problem solution from the initial condition u(r,π/2) = sin([2π/ln2]lnr) --> R = Acos(λlnr) + Bsin(λlnr) and then apply BCs tl;dr: clutched out exam and aced it. Last edited by Unaffiliated: 12-14-2011 at 08:56 PM. Reason: formatting.
12-14-2011, 08:08 PM
#252
The Bored Man
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Quote:
 Originally Posted by Unaffiliated a) heat equation (ut = uxx) with time-dependent source term. had to use eigen-expansion of the heat equation part [u(x,t)] and the source term [s(x,t]. Here s(x,t) = t For some reason I panicked when I had to expand s(x,t) = Σsn(t)cos(λx) and erased everything and tried to find a v(x,t) to get rid of the source term in the HE. Then later on I realized that I was an idiot and that t = Σsn(t)cos(λx) works fine. I didn't get all the way to the final solution because there's a HUGE amount of trivial math to do, but I wrote the rest of the steps of the solution from where I was in English, which should get me big part marks. b) Polar Laplacian urr + (1/r)ur + (1/r^2)uθθ = 0 I couldn't figure out the solution to R-problem in the separation of variables. Apparently it's something to do with the euler equation. Anyway, I just inferred the R-problem solution from the initial condition u(r,π/2) = sin([2π/ln2]lnr) --> R = Acos(λlnr) + Bsin(λlnr) and then apply BCs

 12-14-2011, 08:29 PM #253 STARMAXX Shi Shi Shawww     Join Date: Dec 2006 Country: Posts: 848 vCash: 500 Oh man, this time tomorrow I will be one of the drunkest men on the planet. I've had 4 exams in the past 3 days and 2 of my most important ones tomorrow. Spending 14-15 hours a day studying gets old fast.
12-15-2011, 12:04 AM
#254
Epsilon
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Quote:
 Originally Posted by Unaffiliated Just finished my Partial Differential Equations exam! With 40 minutes left I had only done 3/5 questions -- the others had me confused. Then I suddenly realized what I was supposed to do on both, and flew through them. Should probably end up with 90ish on the exam . I went into the exam with 98% and 96% on my two midterms and 90+% on homework. SO AMPED. Math talk below: The questions I couldn't figure out were: a) heat equation (ut = uxx) with time-dependent source term. had to use eigen-expansion of the heat equation part [u(x,t)] and the source term [s(x,t]. Here s(x,t) = t For some reason I panicked when I had to expand s(x,t) = Σsn(t)cos(λx) and erased everything and tried to find a v(x,t) to get rid of the source term in the HE. Then later on I realized that I was an idiot and that t = Σsn(t)cos(λx) works fine. I didn't get all the way to the final solution because there's a HUGE amount of trivial math to do, but I wrote the rest of the steps of the solution from where I was in English, which should get me big part marks. b) Polar Laplacian urr + (1/r)ur + (1/r^2)uθθ = 0 I couldn't figure out the solution to R-problem in the separation of variables. Apparently it's something to do with the euler equation. Anyway, I just inferred the R-problem solution from the initial condition u(r,π/2) = sin([2π/ln2]lnr) --> R = Acos(λlnr) + Bsin(λlnr) and then apply BCs tl;dr: clutched out exam and aced it.
(keeping in mind that I just finished drinking 8 beers): this sounds about right, at least conceptually. I think you can solve the second problem directly though. Are your functions real or complex-valued?

 12-15-2011, 02:50 AM #255 Larsson 4th Line Boys     Join Date: Jan 2007 Location: Holmdel, NJ Country: Posts: 10,398 vCash: 500 2/3 of the way through my final paper for Social Theory. I don't know how it's possible to write about this stuff for a living.
 12-15-2011, 03:51 AM #256 sandman441 Registered User     Join Date: Jan 2003 Location: ALASKA Country: Posts: 6,756 vCash: 500 Got 2 out of 3 done. Tomorrow is the last one, then I'm off for a month and a half.
 12-15-2011, 03:54 AM #257 hockeydemon05 Registered User   Join Date: Sep 2005 Location: So Cal Posts: 2,654 vCash: 500 Got my results back. Shockingly my worst grade was in Highway Design (86%, which was slightly above the median @ 85). Scored at least one standard deviation over the median on both Chemistry and Fluid Mechanics (SO CLUTCH, I think I got an A in Fluids)
12-15-2011, 10:33 AM
#258
Zaide
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 Originally Posted by tml_4ever Have you ever taken analytical chem? You have to wear little finger things so that stuff from your hands don't affect the weight the things you're weighing and round to 4 decimal places As you can imagine, your yield being off by a little bit can drop you a whole letter grade D:
No, I just started college (CEGEP here in Quebec) and it was simply general chemistry about matter.
Quote:
 Originally Posted by Unaffiliated Zaide, that sucks about your chem exam. At least your mark is still good.
I know my mark is still good, but I aimed for 90%+ so that my difference between my grade and my class average would be like 3 or 4% higher than the SD of the group (If you know the way our final grade is calculated here in Quebec). Now I have to get like 95%+ at the last theoretical exam next monday if I want this. That's a huge blow to my Cote R imo, because I want to apply at med. school, where they ask for a Cote R of 33-34. Chemistry was my chance to even things up because I only have 31 or so in philosophy.

 12-15-2011, 10:58 AM #259 Xelebes Registered User   Join Date: Jun 2007 Location: Edmonton, Alberta Country: Posts: 4,436 vCash: 692 Corporate Finance here we come!
 12-15-2011, 12:09 PM #260 Sensfanman Registered User     Join Date: Jan 2006 Location: Los Angeles, CA Country: Posts: 10,182 vCash: 500 I had a 93 going into my final yesterday. It was a pretty easy exam, I was getting all the questions except the 2nd part of one question I had no idea what to do. With half an hour left, I worked on trying to solve that one question, knowing I had the rest covered. With 5 minutes left I realized there was another page of really easy questions. Instead of the 90 I would have had, I'll probably get a 60, costing me my 4.0 in that course and possibly honours with it. FML.
12-15-2011, 12:52 PM
#261
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Disclaimer: boring math, skip this

Quote:
 Originally Posted by Epsilon (keeping in mind that I just finished drinking 8 beers): this sounds about right, at least conceptually. I think you can solve the second problem directly though. Are your functions real or complex-valued?

You can solve it directly. I just sorta blanked.

separate u(r,θ) into R(r) and Θ(θ)

Multiplying the whole equation by r^2 you get

(r^2)urr + (r)ur + uθθ = 0 (sorry i can't do subscripts but everything after the u is partial derivs)

so then separate u = RΘ and rearrange to get the "R-problem" and the "Θ-problem" (that's what our prof called it)

eventually

(r^2)R'' + (r)R' + (λ)R = 0

rewrite in Sturm-Louiville form

(rR')' + (λ)(1/r)R = 0

so your solutions are given in the form r^μ

where μ is given by μ^2 + λ = 0

so μ = ±i√(λ)

so r^(i√(λ)) ---> R(r) = Acos(√(λ)ln(r)) + Bsin(√(λ)ln(r))

Not a big deal though. Most of the people I talked to just remembered the question from the homework, and just skipped directly from

(r^2)R'' + (r)R' + (λ)R = 0

to the solution

Last edited by Unaffiliated: 12-15-2011 at 12:54 PM. Reason: reformatted math stuff so it doesn't take up too much space on page

12-15-2011, 01:31 PM
#262
ECL
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Quote:
 Originally Posted by Zaide No, I just started college (CEGEP here in Quebec) and it was simply general chemistry about matter.
IMHO, gen chem is the hardest of the chem classes. I thought that Orgo, etc. were all easier.

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12-15-2011, 02:04 PM
#263
Zaide
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 Originally Posted by Jonathan. IMHO, gen chem is the hardest of the chem classes. I thought that Orgo, etc. were all easier.
Don't know for me since I still don't have take those classes. Good sign if that's true I guess. But for me, I had the feeling, for half of everything, that it was just what I saw in Sec. 5 chemistry. The rough part was the interactions between light and matter, and maybe the orbital stuff.

 12-15-2011, 08:27 PM #264 Unaffiliated Registered User     Join Date: Aug 2010 Location: Richmond, B.C. Country: Posts: 10,284 vCash: 500 Well. That MECH exam f***ing SUCKED. I should still pass the final once it's been scaled, though.
 12-15-2011, 09:21 PM #265 JustGivingEr How far we done fell     Join Date: Aug 2009 Location: Hamsterdam Country: Posts: 27,225 vCash: 1125 Just wrote my Calc exam. It was pretty brutal. I was pretty confident I'd get an A in the course but now I'd be thrilled if I got one. The exam was basically the profs being dicks. There were two questions worth a lot of marks that were questions we'd seen a lot of, except with a new twist that I've never seen before. I talked to a couple people after the exam and nobody got both of them and most people didn't get one. Whatever, now just one more to go.
 12-15-2011, 09:27 PM #266 MatthewT Registered User     Join Date: Mar 2008 Country: Posts: 16,592 vCash: 500 Number theory exam tomorrow morning, haven't studied much for it but has potential to good depending on which theorems the prof wants us to prove. Not that I really care anyway
 12-15-2011, 09:49 PM #267 kaiser matias Registered User   Join Date: Mar 2004 Posts: 2,128 vCash: 500 Finished my exams today. All history courses, so essay writing on all five of them. Also got an essay back from my US Sports since 1960 course, worth 40% of my grade. Scored 93% and had the prof ask me to email it to him so he can use it in the future or something. I would think that if I'm being asked for my work then I'm doing something right.
 12-15-2011, 10:01 PM #268 Sergei Goldenhands Used Registerer     Join Date: Feb 2009 Location: Quebec City Country: Posts: 1,954 vCash: 500 I hate fiscal accounting. so many ****ing rules and tax credits to learn by heart. Give me the ****ing Quebec Fiscal Code and I'll make you the perfect income statement, but don't ask me to remember that you can deduct up to \$250/week from your income if you have a disabled kid, \$150 for a kid under the age of 7 and \$100 if he's over 7yo. Good thing I don't plan of becoming an accountant.
 12-15-2011, 10:17 PM #269 Montag DP Sabres fan in...     Join Date: Apr 2007 Location: ...Atlanta Country: Posts: 7,261 vCash: 50 Well, I'm calling it a night wrt studying for Unsteady Aero. I'll have a couple hours before the exam tomorrow morning. I'm guessing it's going to be rough, but luckily I only need a 40% or so.
 12-15-2011, 10:44 PM #270 PZA* ▬▬ι═══════ﺤ   Join Date: Sep 2009 Posts: 1,428 vCash: 500 Bragging about getting A's outside any major of Engineering, Nursing, Computer Science, Pre-med, or Accounting is funny.
12-15-2011, 11:12 PM
#271
RoyBoyCoy
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Quote:
 Originally Posted by Sly Bragging about getting A's outside any major of Engineering, Nursing, Computer Science, Pre-med, or Accounting is funny.
That's cute.

12-15-2011, 11:13 PM
#272
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 Originally Posted by Sly Bragging about getting A's outside any major of Engineering, Nursing, Computer Science, Pre-med, or Accounting is funny.
Stupid Science majors!

 12-15-2011, 11:38 PM #273 Negative Split Registered User   Join Date: Jan 2011 Country: Posts: 49 vCash: 500 Just missed out on an A+ in two different classes by less than 5 points (out of 1000). Plus I just turned in the final English paper of my college career, and when I looked at the other essays in the pile they were all really well written and deeply thought out. Rough day.
 12-16-2011, 12:45 AM #274 sandman441 Registered User     Join Date: Jan 2003 Location: ALASKA Country: Posts: 6,756 vCash: 500 Blech I hate tests, but I'll end up with atleast 2 B's.
 12-16-2011, 06:49 AM #275 Satan depression cherry     Join Date: Apr 2010 Location: @brelyt Country: Posts: 50,348 vCash: 69 Graphics exam today, then flying back home at 3... and I don't even get in until 1:30 am But it feels great to (almost) be done!

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