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How to change the order of a double integral 

blackpenredpen
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Change the order of integration in a double integral, ft, integral of ln(1+x)/x using power series,
integral of ln(1+x) from 0 to 1, www.wolframalp...
how to get pi^2/12, • 1-1/4+1/9-1/16+... (z...
blackpenredpen,
math for fun,
blackpenredpen..., / blackpenredpen ,
blackpenredpen@gmail.com

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28 сен 2024

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Комментарии : 100   
@YanLobianchi
@YanLobianchi 6 лет назад
DOUBLE INTEGRAL A BEGINNING FINALLY
@rodrigosuarezcastano732
@rodrigosuarezcastano732 6 лет назад
Will you ever upload the full version of the outro song? Also please make more differential equations, they were really awesome and i'm kind of struggling with the subject right now, anyway, great videos, you make the most scary questions so understandable is amazing
@blackpenredpen
@blackpenredpen 6 лет назад
Here's the original. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-gBLjRz1xX_8.html My gf might play the full version one day. And when that happens, I will let you know.
@sergiokorochinsky49
@sergiokorochinsky49 6 лет назад
Nice example about how to define a region of integration. The explanation was a bit confusing though. I would have drawn the triangle right from the beginning, explain the original limits of integration by "painting" the triangle with horizontal lines, and then introduce the new limits of integration with vertical lines. Anyway, you ended up using the series, so I can't see the benefit of changing the order of integration...
@tomatrix7525
@tomatrix7525 4 года назад
Sergio Korochinsky yeah, we could just integrate in dx, and then that ans in dy, using series again for the ln...I agree the swapping of integrals was futile but still cool
@rasraster
@rasraster 3 года назад
When you look at how double integrals are defined, he's actually right. Step 1, set y; step 2, let x range from 0 to that y. Repeat for the next largest y.
@adrianfletcher8963
@adrianfletcher8963 6 лет назад
Calc 3 let's goooo
@adrianfletcher8963
@adrianfletcher8963 6 лет назад
Also what allows you to interchange the summation and the integral? I forgot the reasoning
@blackpenredpen
@blackpenredpen 6 лет назад
Fubini's Thm.
@andresxj1
@andresxj1 6 лет назад
Poor Tonelli...
@juliangst
@juliangst 6 лет назад
I have 2*ln(2)-1 for the 2nd integral
@Davidamp
@Davidamp 6 лет назад
log property, the 2 goes in as a power
@herbcruz4697
@herbcruz4697 3 года назад
2*ln(2) is the exact same thing as ln(4). You can re-write 2*ln(2) as ln(2^2) by using the Power Property of Logarithms, in the opposite direction (One of the properties of logarithms is that, if you have the log of something raised to a power, then you can take the exponent, and pull it out in front of the log (In this case, we're using that property the other way around)). Then 2^2=2*2=4, so that's why we have ln(4).
@juliangst
@juliangst 3 года назад
@@herbcruz4697 I know that already but thanks xD
@MA-bm9jz
@MA-bm9jz 6 лет назад
That problem from the coment can be easily done using the taylor expansion for ln(1+x) and than divide that by x and integrate from 0 to 1 and you get 1/1^2-1/2^2+1/3^2-... And we know that 1/1+1/2^2+1/3^2+.... Is pi^2/6 and from that you deduce that that series which is exactly like sum of squares inverse but it's alternating with +- is pi^2/6(half of the original series)
@drioko
@drioko 2 месяца назад
i watched 5 different videos i only understood with your video
@Neji641212
@Neji641212 6 лет назад
Mr blackpenredpen, I`ve problem with understanding nyquist stability criterium. Would you mind showing, how to create nyquist plot and properly understand what is shown there. I don`t really get it.
@Hobbit183
@Hobbit183 6 лет назад
Can u do some basic multivariable videos for students who finished calc 2
@sumspiew
@sumspiew 2 года назад
blackpenbluepen
@alek11-37
@alek11-37 3 года назад
I figured the integration limits without a picture
@therealAQ
@therealAQ 6 лет назад
Do you know for what N is Ln(N) transcendental?
@nejlaakyuz4025
@nejlaakyuz4025 6 лет назад
therealAQ e^e of e^pi seems good to me.
@budtastic1224
@budtastic1224 6 лет назад
Am I mistaken? But why not use U-sub for ln(x+1)/x
@MarioFanGamer659
@MarioFanGamer659 6 лет назад
You need to find a way to eliminate all instances of x when doing a substitution (or as bprp would say, no X can exist in the U-world) and a u-substitution with u=ln(x+1) would result in ln(u)/x * (1+x) du = ln(u)/x du with an x still having in the numerator.
@cherrytaly9765
@cherrytaly9765 6 лет назад
11:15 wondering!
@JordHaj
@JordHaj 5 лет назад
1:02 I actually want to have dy first. Y? Because *I WANT* to have.
@amazinglittlekuin8929
@amazinglittlekuin8929 5 лет назад
Is this an April fools joke!
@blackpenredpen
@blackpenredpen 5 лет назад
why?
@MMMM-es6ur
@MMMM-es6ur 5 месяцев назад
Why i cant understand that i try but I always fail🥲
@ゴテンクス-q8q
@ゴテンクス-q8q 6 лет назад
Can you do a triple integral
@ano.g.6217
@ano.g.6217 3 года назад
Yes
@volt5481
@volt5481 3 года назад
How is the integral from 0 to 1 of ln(1+x) equal to ln(4)-1 and not ln(2) ? Am I missing something ?
@archimidis
@archimidis 6 лет назад
I solved it without changing the order. The inside integral is just a function of y, let's call it f. We can integrate f by parts, just like lnx, to get yf(y) minus the integral of yf'(y)=ln(1+y) From 0 to 1 we get f(1) minus the integral of ln(1+y) where f(1) is just the integral of ln(1+x)/x and the rest is the same.
@Anteater23
@Anteater23 6 лет назад
Not all heroes wear capes. Do you teach at a university? If you do I want to travel the world and study at your uni.
@sUpErTrEkKiE100
@sUpErTrEkKiE100 6 лет назад
I think he's a highschool teacher
@RishaadKhan
@RishaadKhan 3 года назад
@Mustafa Finn Bot.
@alexmates614
@alexmates614 6 лет назад
I can't stop watching ur vids. They're awsome. Thanks, and greetings from a spanish mathematician
@blackpenredpen
@blackpenredpen 6 лет назад
Thank you!!
@margintoosmall925
@margintoosmall925 6 лет назад
The video is 11:11 :O Make a wish!
@margintoosmall925
@margintoosmall925 6 лет назад
This was more complex and fascinating than I originally thought. Wow!
@protocol6
@protocol6 6 лет назад
+1 for the Pierre de Fermat reference in your name.
@blackpenredpen
@blackpenredpen 6 лет назад
I like your name.
@margintoosmall925
@margintoosmall925 6 лет назад
Thank you!
@synergetic4d
@synergetic4d 6 лет назад
Excellent videos 3blue one brown is also good channel. I still find it hard to understand what you are saying sometimes. Could you explain in general what double and triple integral means geometrically?
@andrewpod5693
@andrewpod5693 6 лет назад
Wouldn't you mind expplain rules when i can swap Integration order and rules when i can swap integration and summation?
@Reciter_Omar.Elhajjy
@Reciter_Omar.Elhajjy 3 года назад
Thank you so much 🙏
@tomatrix7525
@tomatrix7525 4 года назад
Ln(1+x)/x can be integrated using parts, or DI method. Think of it as x^-1(ln[1+x] . Now we diffrentiate the log part using the DI method, and integrate the x^-1 . This works out nicely as easier perhaps than power series...
@MarioFanGamer659
@MarioFanGamer659 3 года назад
--Doesn't work out as if you differenciate ln(1+x)/x, you get (x - x*ln(x+1) - ln(x+1))/(x³ + x²) which leads to nowhere.-- Edit: I now see what you mean. It still doesn't work out because will end up integrating ln(1-x)/x which yields a polylogarithm which is defined by sums.
@McShat
@McShat 6 лет назад
you're a genius
@daimao7392
@daimao7392 6 лет назад
Bravo!!
@MarceloKatayama
@MarceloKatayama 6 месяцев назад
Is it possible to figure out the bounds of integration without having to graph the region of integration?
@pratyushyadav3947
@pratyushyadav3947 9 месяцев назад
why the limit of y cannot go from o to x when we swapped to dydx ? please tell as i took it from 0 to x and i am getting only ln4-1 as final answer.
@kennethgee2004
@kennethgee2004 4 года назад
at thge end you asked if we need +C. The answer is absolutely NO!. This is a proper integral so we are evkuating the area under the curve. The +C would cancel out, so to put +C is wrong.
@toasticide816
@toasticide816 6 лет назад
Nice, close to 100k subscribers! Early congratulations. Love this channel
@blackpenredpen
@blackpenredpen 6 лет назад
Louis Moore thank you!!!!!
@NonTwinBrothers
@NonTwinBrothers 3 года назад
Damn, so many of these are underviewed
@link_z
@link_z 6 лет назад
One of my favorite videos! Thanks!
@15schaa
@15schaa 6 лет назад
Really showing integrity.
@blackpenredpen
@blackpenredpen 6 лет назад
what do u mean?
@15schaa
@15schaa 6 лет назад
Integral-ty
@blackpenredpen
@blackpenredpen 6 лет назад
i see!
@ゴテンクス-q8q
@ゴテンクス-q8q 6 лет назад
Great video
@chrislarson5097
@chrislarson5097 6 лет назад
when doing it by myself, i started with differentiation under the integral sign where I(a)=$(0,1,($(0,y,ln(ax+1)/x)dx)dy). then, skipping a bit you can do yourself, i found I(1)=$(0,1,[(1+a)ln|1+a|/a]-1)da-. from there, I used the same method as previously, and stated F(b)=$(0,1,[(1+a)ln|1+ab|/a]-1)da. solving that, (subbing u for 1+ab stumped me for a bit,) i ended up getting F'(b)=1, F(1)=%(0,1,1)db-%(0,1,1)da=0. if i got 0 as my final answer, can anyone follow my process and tell me where I went wrong? I know i didn't give specifics, but between what steps did i make my mistake? id go into detail but it takes up a page and a half.
@khurramshahzad2164
@khurramshahzad2164 6 лет назад
how do evaluate integral 5t^2-3t+18/t(9-t^2) shoes limits 2 goes to 1 please jaldi solution btain
@mohit9798
@mohit9798 4 года назад
can you find the double integral of modulus (xy)dxdy over region ellipse and circle.
@mohamadazzamcherahim5773
@mohamadazzamcherahim5773 6 лет назад
iterated integration?? o.o
@diegotejada55
@diegotejada55 6 лет назад
Is this a Papa Flammy reference?
@blackpenredpen
@blackpenredpen 6 лет назад
? why?
@diegotejada55
@diegotejada55 6 лет назад
blackpenredpen it's a joke, he made a meme video yesterday, where he was fighting Lebesgue so that he could interchange the order of integration without any restrictions
@blackpenredpen
@blackpenredpen 6 лет назад
OH yea that one!!!
@willbishop1355
@willbishop1355 6 лет назад
Great problem! Being 10 years removed from Calculus BC I had forgotten the power series for ln(1 + x)...
@MustafaTAli
@MustafaTAli 6 лет назад
Please can you solve this integration :- root Sin(x) dx ??
@awdwadawdwadw8651
@awdwadawdwadw8651 6 лет назад
Cool jacket where id u get it? :)
@yaleng4597
@yaleng4597 6 лет назад
wow
@Patapom3
@Patapom3 6 лет назад
Great!
@gillkhaas
@gillkhaas 6 лет назад
nice, thank you so much!
@sivad1025
@sivad1025 6 лет назад
This proof is absolutely beautiful!
@trambakphysik7
@trambakphysik7 4 года назад
Very well explained, always enjoy your videos
@marcioamaral7511
@marcioamaral7511 6 лет назад
Can I give you a list of hard limits to do without l'hopital unless you need to? I recommend you to get B.Demidovitch problems book
@blackpenredpen
@blackpenredpen 6 лет назад
ok!
@dreadk5594
@dreadk5594 6 лет назад
The answer to the first integral was already given as a condition for evaluating the double integral, but glad you worked out the series part.
@blackpenredpen
@blackpenredpen 6 лет назад
Balanar Johnson Yes. That part is really cool too
@BlokenArrow
@BlokenArrow 6 лет назад
Isnt the area of the icosoles right triangle one half?
@Gold161803
@Gold161803 6 лет назад
BlokenArrow Yes, but we're integrating the value of the function over that input region, not just computing its area :p
@dominikstepien2000
@dominikstepien2000 6 лет назад
Where is a link to the video about power series for ln?
@Gold161803
@Gold161803 6 лет назад
dominikstepien2000 Search his videos for the "best friend", which should be the formula that says the sum of x^n as n goes from zero to infinity is 1/1-x [on interval of convergence]. Replace x with (-x) and integrate and you should get the ln(1+x) power series
@yeonhojung7185
@yeonhojung7185 6 лет назад
black pen blue pen :-3
@blackpenredpen
@blackpenredpen 6 лет назад
Yeonho Jung lol
@mattgsm
@mattgsm 6 лет назад
10:21 YOU used "is nothing but" like Flammable maths does! What does that phrase even mean? People are nothing but atoms but saying "integral is nothing but..." Is like saying "I am nothing but hungry" which doesn't make much sense
@blackpenredpen
@blackpenredpen 6 лет назад
I dont know if I can give a good explanation to this... I think I meant to say this isn't anything hard since the answer is...
@mattgsm
@mattgsm 6 лет назад
blackpenredpen oh! I just wondered why you both say it. Who copied who. I'm not being rude. I'm sorry xD
@turkishwagnerian
@turkishwagnerian 6 лет назад
Upper bounds are invisible in integral !!! I didn't understand the integral in first, therefore Video has wrong !
@imcry3408
@imcry3408 6 лет назад
Hey blackpenredpen, Nice Video! I've recently got a problem on an integration problem and I cannot figure it out. I would like to ask if you could try this problem. :( Evaluate the integral from 0 to infinity of (exp(3x) - exp(x))/[x(exp(3x) +1)(exp(x)+1)] Thank you
@nakedbanana
@nakedbanana 6 лет назад
I have little question when I calculate the integrate ln(1+x) I used the U substitution to let U=1+X to transfer the question became ln(u) then integration by part but when I put the boundary in the answer why my answer is different with yours?? Then I use integration by part directly let u=ln(1+X) du=1/(1+X) so I can get the right answer finally was that wrong if I use integration by part so I can not use U substitution first?? Or do i miss to consider other condition?
@MarioFanGamer659
@MarioFanGamer659 6 лет назад
(1+x)*ln(1+x)-(x+1) really is the anti-derivative of ln(1+x). That being said, it might be that you have taken the boundaries for the u-substitiution (2 and 1) instead for x (1 and 0). If you put the values 1 and 0 into the anti-derivative, you get 2*ln(2) - 1 or ln(4) - 1. Or it could be that you don't know that prefactor A of the logarithm of number B is equal to the logarithm of B to the power of B, that a*log(b) = log(b^a) which might explain why the result is different.
@nakedbanana
@nakedbanana 6 лет назад
Thx for the reply, I was just wondering why there are two answers if i use U substitution then integration by part will get the solution is (1+X)ln(1+X)-(1+X) but if use integration by part directly will come out (1+X)ln(1+X)-X both of them put the boundary(1 and 0) will get the final answer ln(4)-1 is the Integral constant caused the -1 become the gap between two integration ways?
@MarioFanGamer659
@MarioFanGamer659 6 лет назад
@nakedbanana: I'm pretty sure, you made a small mistake. You can make a u-substitution with u = ln(1+x); du = dx/(1+x) and get a valid but the resulting integral becomes ∫(u*e^u)du = e^u * u - e^u or with x, ln(x+1) * (x+1) - (x+1) which is the same as with a substitution with u = 1+x.
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