EPTBut hell, that ODE is so piss easy to solve (I have no idea what exactly AB calc is though so you might not have covered this).
Nice trick malongo, I would've just brute-forced the thing and ended up with a page of mess =p
AB Calc Help proof ( i think?) - Page 2
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Turbovolver
Australia2346 Posts
But hell, that ODE is so piss easy to solve (I have no idea what exactly AB calc is though so you might not have covered this). Nice trick malongo, I would've just brute-forced the thing and ended up with a page of mess =p | ||
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Malongo
Chile3468 Posts
since sinPi/4=√2/2 just follow the lines 1 by 1 And the lines where almost all copy paste -_-' | ||
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Malongo
Chile3468 Posts
On March 13 2009 15:08 Turbovolver wrote: LOL, the original problem was written so unclearly, because as far as I can tell the 3 and the -2 have already been pre-multiplied. You should just be adding the three things together, not subbing them in to y'' = 2y' - 3y. But hell, that ODE is so piss easy to solve (I have no idea what exactly AB calc is though so you might not have covered this). Nice trick malongo, I would've just brute-forced the thing and ended up with a page of mess =p Actually he doesnt have to solve the ODE just prove that y satisfy the ODE. I love trigonometry  | ||
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Hypnosis
United States2061 Posts
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Turbovolver
Australia2346 Posts
On March 13 2009 16:24 Hypnosis wrote: isnt y'' the second derivative of y? this is stupid problem that exists to look complicated when its really a stupid problem with no real solving reason... calc isnt hard it just looks hard lol. Yep, exactly. Also Malongo, that trig isn't necessary for the solution, it just makes it a lot cleaner. You probably realise that but whatever. | ||
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Bitter
United States2 Posts
luckily with a little diff e q ... r^2-2r+3=0 r= 1 +/- √2i gives the general formula: y = c1 e^x cos√2x + c2 e^x sin√2x so as long as the c1 and c2 are correct everything seems right so go ahead and assume for sure that it is in fact cos√2 * x and etc for whoever wants to type everything out. It is simply derivative of first multiplied by second + first times derivative of second over and over and over. now this is annoying to write out so i would make a variable v=sin√2x and w=sin√2x and you end up with -2v-2w=v''+w'' which is true. lemme know where you are having problems (yay me for first post on teamliquid being a calc post ). | ||
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ninjafetus
United States231 Posts
http://www.webpages.ttu.edu/jmillhol/calcproblem.pdf (rotate clockwise to read :p) | ||
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Hypnosis
United States2061 Posts
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Cloud
Sexico5880 Posts
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ninjafetus
United States231 Posts
On March 14 2009 06:14 Hypnosis wrote: So it's hardly a proof. Unless your trying to prove that something is true using the limit h goes to zero formula.. Well, it depends on what the question is. Since the question was "show that this y satisfied this ODE", you could call it a proof to take the derivatives and plug it in. It doesn't need deltas and epsilons or some fancy theoretical framework to be called a proof; it just needs to verify some statement. Besides, you could argue the "limit as h goes to zero formula" is not a rigorous proof either, since you haven't rigorously justified the limit. What it comes down to is the framework you're expected to solve the problem in. | ||
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