Stupid Definition and 300 Threads

Hey all, i just lost a TON of points on a test for solving a problem in a way that is apparently invalid. The problem was verify that y(x) = x+1 is a solution for dy/dx = y*y-x*x-2x; y(0) = 1. i plugged y = x+1 into the right side of the second equation, got dy/dx = 1, integrated...

But right now all math feels like is, "Here is a bunch of numbers and funny looking symbols, now do this step, then this, now do that because it just works, no questions asked. Just do it this way, understood?" And then the word problems come at me and I'm clueless, unless it resembles the one...

Hi, as you all know one can write the Maxwell-equations in covariant form, namely: \partial_a F^{ab} = \frac{4\pi }{c} j^{b} and \partial_a G^{ab}=0 where \textbf{G} is the dual Tensor to \textbf{F}. Now the two simple questions. I can see that they are invariant, because I...

Homework Statement I need a way to write the following series in a sum: \frac{1}{2} + \frac{1}{4} + \frac{1}{32} + \frac{1}{64} + \frac{1}{1024} + \frac{1}{2048} + ... If you look closely you can see a 2^n pattern in there: \frac{1}{2} + \frac{1}{4} + \frac{0}{8} + \frac{0}{16} +...

If you have a phosphor such as ruby (Cr:Al2O3) and you excite it with a light source near its main pump band (~556nm) then you should see emit light with a difference in color from the source light, correct? For example if I shined a green light onto this piece a ruby, it should appear red...

Here is a question of practical philosophy (the best kind, in my opinion). How does one maintain a position of authority without becoming stupid in the process? When you are in a position of authority, you have to keep up the impression that you are wise--that your decisions, judgments, and...

rank amateur here - as i currently understand it, dark energy does not react with anything so we cannot detect it directly. DE is deduced from macro scale observations of the movements of distant galaxies, which arent behaving as they should given the amount of observed mass. (i hope all that...

Division by zero is undefined...but why doesn't somebody just define it? Like they did with root (-1).

Homework Statement The points A and B have position vectors a = (2,2,1) and b (1,1,-4) respectively relative to an origin O. (im using column notation for shorthand) Prove that OA is perpendicular to AB Homework Equations The Attempt at a Solution To be perpendicular the...

Okay; so here is a screenshot of my PCs (it is a desktop) info. Here is what I want to know: 1) 256 MB is pretty small isn't it? My Macbook has 4GB 2.) Where can I look to see if I can fit more RAM in my PC? I assume that is not the max I can fit? 3.) Assuming I am not 100%...

when we try to build the gauge theory of gravity we needs the vierbeins fields and spin connections fields. In the case we take them independent, which are the kinetic terms for two fields? or in other words, is the commutator of covariant derivatives the kinetic term for vierbeins and for spin...

Homework Statement Hi I have to say true or false, and then demonstrate my answer "if taking any 3 Real numbers (a, b, c), we have at least 2 of the same sign" For me its true, i was thinking of creating a triplet (x, y, z), where x=1 if "a" positive, x=0 if "a" negative, same for y...

Homework Statement I am trying to solve this basic calculus problem, but I can't figure out the last step. It doesn't make sense to me. I know I'm just being an idiot and not thinking of it. This actually has little to do with calculus and more to do with basic algebra. Doh...

1. In Poker: A) A flush is 5 cards of the same suit not in any order. How many flushes are possible? B) A full house is 3 of a kind plus a pair. How many full houses are possible? 2. n C r (That's all I can think of right now) 3. For A) (13 C 5) / (52 C 5) = 33 / 66640...

It’s about conscience, stupid; not consciousness Why has the English language not coined a word that speaks to the concept of conscience without the confusion associated with the concept of consciousness? There must be a psychological aspect here. What would Freud say? Freud’s...

Homework Statement (secx-1)/x^2 limit x--->0 Homework Equations secx=1/cosx (1-cosx)/x=0 The Attempt at a Solution I have done obvious thing, solved to make secent cosine and got common denominators in the top portion of the fraction, then subtracted. Ended up with...

okay, ill try to explain this situation a best as i can. so, i started talking to this girl. I am not quite sure how it all started but i seemed cool so, i went with it. a cool thing (i thought so) was the fact that we hang out with a lot of the same crowd. so i got to see her often and see...

[SIZE="5"]SOLVED Homework Statement A stubborn, 120 kg mule sits down and refuses to move. To drag the mule to the barn, the exasperated farmer ties a rope around the mule and pulls with his maximum force of 770 N. The coefficients of friction between the mule and the ground are µs = 0.8...

How might one prove that for any degree n polynomial p(x) with coefficients lying in a field k, there exists any nxn matrix with entries in k with characteristic polynomial p?

Homework Statement A 60kg person floats vertically in a water pool with just her head, of volume 2.5L, exposed. What is the average density of her body?Homework Equations Archimedes: F = rho*V*g mass = rho*V The Attempt at a Solution I got this problem on my midterm and I'm pissed off that I...

Okay, so say I have an equation that looks like this: 9y - 4x + 5 = 0 and I wan to move every thing but the y over to the right hand side. When it gets to the last step and looks like this: 9y = 4x - 5 When I move 9 over to the other side, does it's sign change? I know the other...

If we add a third observer to the twins paradox at the turnaround point (at rest with earth), and with a clock that was synched with the other two when the ship left earth, what will that clock read when this third observer sees the ship turn around? Assuming v= 0.8c, distance = 8 ly...

if something is moving at a wall with a given velocity. and is in contact with the wall for say 0.2 seconds. the chance in velocity for those 0.2 seconds would be (-) the velocity it hit it win?

why is it that the feynman diagram illustrating Bremstrahlung radiation has three vertices; basically an electron decays into a)a photon which recoils the nucleus and b)a virtual electron WHICH THEN decays into another photon and an electron of lower energy. why can't the original electron...

Upset :( This is the post where I'm going to sound like a stupid immature typical teenager, so stop reading here if you don't want to hear it. So, I'm sitting in some week long holiday course that I just now finished, in the seat that looks straight out the door and into the corridor. I...

I think I am a bit confused here. How does higher current output power supply differ from high voltage supply? Is it just the internal resistances of the supply? For example a Lithium Ion battery from an Alkaline battery. I am asking coz, I was reading about static. Your body can charge...

Homework Statement factorise x^2+3x=2 Homework Equations erm... The Attempt at a Solution (x+2)(x+1) book says (x+1)(x+2) aren't those answers the same? i know it's a stupid question but i want to make sure I'm getting this right

So in a calc 2 exam, you gloss over all the derivatives questions and get to integration and series. You get the really tough integrals, but you miss the grade-boosting derivative question (10%/100)?! So I've never gotten lower than 95% on a math midterm, but now I'm getting 85%~. Look at how...

Homework Statement For the life of me, I can't decide whether the method below is correct and it's making me feel really stupid. Homework Equations Simple matter of an algebraic identity. Is: \frac{\partial L}{\partial(\frac{d\overline{A}}{dx_{\mu}})} = \frac{\partial L}{\partial...

I'm currently a 3rd year student majoring in physics and will probably end up with a minor in math. I'm having a major crisis tryin to decide what to do with my life. I'm currently taking upper-div mechanics, but the class is pretty boring. I'm thinking about leaving physics also because...

[SOLVED] Stupid question about Clebsch Gordan I know that \sum _{m_1,m_2}|<j_1m_1,j_2m_2|jm>|^2 = 1 But is \sum _{m_1,m_2}|<j_1m_1,j_2-m_2|jm'>|^2 = 1 ? I have tried to justify this by using a CG calculator and so on, but I just can't figure out why :S I think that doesent...

[SOLVED] Simple Optics - being stupid?! Homework Statement There's an object 1.5m from a white screen. What is the focal length of a lens needed to form a real and inverted image on the screen with magnification of 4.0? How far from the object should the lens be placed?Homework Equations...

I was just asked "Are salt and sand heterogeneous or homogenous mixtures?" I can see that sand is heterogeneous, but why is salt heterogeous? Casey

So here is what I want to do: I have an Ipod synched to the Itunes Library on my PC I wish to synch it with my Macbook. To do this I need to erase it and replace its contents with the contents of my Macbook's Itunes Library. There is nothing in my Itunes Library so I wish to move all...

Sorry, but this time I really must rant. I was watching the travel channel just now. This is the SECOND program I have seen on the travel channel like this. It’s a show called art attack. Sounds cool? I thought so...until I started watching. This bozo is literally screaming the entire show. It...

Homework Statement I am trying to get used to engineering prefixes and such. I would like to come up with a general way to reduce garbage composite units like Mg/ms into proper units. Anybody have a general way. I know that my end result is to have no prefixes in denominator (except kg)...

On Thursday afternoon, we got heavy snow all afternoon and into the night. We got about 7 inches of snow, but the roads were completely snow covered. Cars on the highway were only going as fast as 18 mph and they were sliding all over the place. What does the mall do? Stay open despite there...

For some reason, I can't work out how to set every element of an array to the same value in a single line, in C#. For example, I can't do this: char[] array_of_chars = new char[limit]; array of chars[] = X or: char[] array_of_chars = new char[limit]; array of chars[0:limit] = X So...

Homework Statement Okay, this would be easy if it hadn't been 15 years since undergrad quantum. Here goes. I'm finding the energy spectrum of a Heisenberg "two-electron ferromagnet", if you will, with a Hamiltonian described by H=-J\hat{S_1}\cdot\hat{S_2}-h(\hat{S_{z1}}+\hat{S_{z2}})...

I really don't know that much representation theory or group theory. I was looking at Garrett lisi's presentation, and I was looking at the 3d root system of g2. It struck me that it looked similar to a dodecahedron inscribed in a cube. Now, I do know that the dodecahedron group, and the...

I find http://news.yahoo.com/s/afp/20071106/od_afp/britainlawsoffbeat, especially about the clerk in a tropical fish store! I'm sure there are plenty of very silly laws here in the US as well. No civilization is immune to such stupidity. :) Zz.

Homework Statement An alien form of frog with a mass of 1.5kg (on a planet with an unknown acceleration of gravity) jumps up from his lilly pad at a velocity of 4.0m/s. If the frog reaches a maximum height of 15m, what is the force of gravity on the frog on this planet? It's a stupid...

I'm kinda confused about atoms. Basically when particles came into existence, they were affecting other particles so they were being "seen", which would allow them to have a position so they could come together to form atoms, right? I'm so confused about atoms after learning about...

Is this the correct way to use the Tabular Method for \int x^2e^{-5x}dx repeated diff: x^2 2x 2 repeated Integration: e^{-5x} -\frac{1}{5}e^{-5x} \frac{1}{25}e^{-5x}...

[SOLVED] Stupid Buoyancy, this is getting ridiculous. A hollow sphere of inner readius 8cm and outer radius 9cm floats half submerged in a liquid of density 800kg/m^3. What is the mass of the sphere and the density of the material it is made from. \sum F=0 \Rightarrow mg-F_b=0 \Rightarrow...

So, I find myself without the AC adapter for my laptop and I need power. My adapter is rated 19.5v 4.7a. I have an adapter from an older machine (same manufacturer), rated 19.5v 3a. The physical connection to the laptop is the same. Will I damage the laptop and/or the battery if I...

Personally i don't think evolution is stupid. I was watching a documentary with this title out of interest. You can watch the full documentary here: h**p://tv-links.co.uk/video/9/5566/8296/53218/76984# (If you copy and paste the link and replace the *s with ts it should work, if not...

grad students that should know things by now (like me!): [though in my defense, I have not had any GR yet, only what I've picked up in some books] My 2 questions: The effect of our time distortion from being near the Earth is cool and all, can I assume we have a similar GR effect from...

So I was reading a journal article and I saw the phrase "electrostatic wave", and I became somewhat disgruntled and ranted a little bit to the guys I share an office with, since the phrase is seemingly an oxymoron...'electrostatic' implies a time invariant field and therefore a 'wave' cannot be...

It's one basic question about nuclear disposal that I have never understood. Nuclear "fluel" like Uran, etc comes from nature - right ? The way nuclear fuel is produced is by increasing the consentration of nuclear material - right ? As the nuclear fuel is used and energy is taken out...