 # Obnoxious

Senior Members

219

## Everything posted by Obnoxious

1. ## Ordinary differential equations question

Okay, so basically, I have to actually work out the expression and solve for r? $-Ar^2\sin(rt+b) + K_1Ar\cos(rt+b) + K_2A\sin(rt + b) = 0$ as in expand the thing with trig identities and mush out an answer? There's no easy way?
2. ## Ordinary differential equations question

In the equation: $\frac{d^2x}{dt^2} + K_1\frac{dx}{dt} + K_0x = 0$ Can someone please explain to me how I'm suppose to be able to use the trig answer $x=A\sin(rt + b)$ or $x=A\cos(rt + b)$ to get to the characteristic equation? Everytime I try to mush the equations around I get stuck at this junction: $-r^2x + K_1Ar\cos(rt + b) + K_0x = 0$ or $-r^2x - K_1Ar\sin(rt + b) + K_0x = 0$ I seriously need some help on this as I'm learning this stuff on my own, and therefore have no professor to turn to with questions.
3. ## What exactly is "sum over path?"

I read about Richard Feynman's theory of sum over path in a book early this year, but I still don't exactly understand it - just how does he assign numbers to each different path an object could take and cancel out all but one path?
4. I'm still in high school, so I get to take community college courses (namely at East Los Angles Community College and Pasadena Community College) for free (w00t California)!!
5. Oh well, I guess it's about time I find myself a job...Oh well, at least I could still take community college courses for free.
6. Damn this price of education!! What happened to American socialism?!?!
8. Not the London one.
9. Can someone please explain to me how it was derived that gravitons travel at the speed of light?
10. Is Ozone polarized?
11. as in angular momentum = displacement vector x linear momentum Can someone please explain to me what the displacement vector is? I tried looking on wiki, but to no avail.
12. Can someone help me find the volume of a torus? I understand how to find volume with the integral, but the torus is giving me sufficient trouble. Worse yet, the calculus teacher at my school refuses to answer my questions because I'm not in his calculus class.
13. Yeah, that's what I meant, thanks!
14. No, I mean f of a real number is another real number. But I have no idea how to make the funky looking R with Latex
15. Is the set of functions: {$f® = R |\frac{df}{dx} + 2f = 1$} a vector space? I said no because it doesn't seem to have a zero vector, but I'm doubtful of my answer. Can someone help me prove its vector space validity (or lack thereof)?
16. Yeah, it was suppose to be the vector a b c is a subset of R³... But I got it! Thanks!
17. Can some please explain to me why $\{a + b + c = 0 | a,b,c \in R^3\}$ is a vector space but $\{a + b + c = 1 | a,b,c \in R^3\}$ isn't? And how do I get the {} to show up?
18. Doesn't that de Broglie wave thing hint that light has mass? $\lambda = \frac{h}{mc}$ Where the lambda is wavelength, h is the Planck constant M is the mass C is the speed of light
19. ## Will Hurricane Rita be Another Katrina?

It's suppose to be worse, because Katrina just hit a corrupt town, but Rita is planned to destroy Galveston and in doing so, knock out 1/4 of America's oil producing industries. Expect a ridiculous oil hike boys!
20. ## Magic The Gathering & Dungeons & Dragons...

LOLOL it's a gurlz!!! OMG OMG </net nerd> Yep, D&D was fun, but time is of essence now, and I have no extra time for any fun.
21. Bush isn't exactly stupid...
22. ## Where is Sayonara....again.

LOL irony (Sayonara is gone)
23. ## Mildly racy short story poking fun of math

Yeah, remember girls, always keep your brackets on, especially if you're convergent. And don't integrate with anyone you don't know, and try to avoid integration by parts!
24. ## Can someone show me the steps of deriving...

I was given $y = e^x$ So I did this! $\ln y = x \ln e$ $dx/dy = 1/y$ $dy/dx = y$ Am I making some illegal moves?
25. ## Can someone show me the steps of deriving...

$f(x) = e^x$ I keep getting the silly answer of just X, when I know it is $e^x$
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