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Mathematics 17 Online
OpenStudy (anonymous):

General solution

OpenStudy (anonymous):

I can help u

OpenStudy (anonymous):

OpenStudy (michele_laino):

Hint: I can rewrite your equation as follows: \[\frac{{\sqrt {1 + {y^2}} }}{y}dy = - \frac{{\sqrt {1 + {x^2}} }}{x}dx\]

OpenStudy (anonymous):

i tried doing it but i am having a difficulty in integrating it

OpenStudy (xapproachesinfinity):

what did you try?

OpenStudy (anonymous):

i tried supposing 1+y as t and 1+x as u and removed sq rt and instead place the power 1/2

OpenStudy (xapproachesinfinity):

you mean U sub but why did you do t=1+y while we have 1+y^2 under the radical

OpenStudy (xapproachesinfinity):

try \[t=1+y^2 ~\Longrightarrow dt=2ydy\]

OpenStudy (anonymous):

sorry forgot to type it

OpenStudy (anonymous):

but my instructor told me that im doing it all wrong

OpenStudy (anonymous):

i supposed the same thong

OpenStudy (xapproachesinfinity):

hmm then try by parts

OpenStudy (xapproachesinfinity):

hmm i believe that sub works as well, your instructor may be pointing to something else

OpenStudy (anonymous):

here have a look

OpenStudy (xapproachesinfinity):

I would actually attempt integration by part first

OpenStudy (anonymous):

OpenStudy (xapproachesinfinity):

hmm you the whole thing as t i suggested a different thing if you paid attention \[1+y^2=t \Longrightarrow y=\sqrt{1-t}\] i see why your prof said you got it wrong

OpenStudy (anonymous):

im not good at integration :(

OpenStudy (xapproachesinfinity):

dt=2ydy so the integral of the LHS becomes \[\int \frac{\sqrt{t}}{2(\sqrt{1-t})^2}dt=\frac{1}{2}\int \frac{\sqrt{t}}{1-t}dt\]

OpenStudy (xapproachesinfinity):

that's what you get after substituting try it now

OpenStudy (anonymous):

but how did we came up with this ? can explain how we had it

OpenStudy (xapproachesinfinity):

well we set t=1+y^2 so y=sqrt{1-t} we have dt=2ydy so dy=dt/2y our integrand is sqrt(1+y^2)/y substituting y and 1+y^2 we get sqrt{t}/sqrt{1-t} now replacing dy by 1/2dt/y which the same as 1/2 dt/sqrt{1-t} and you get what i did

OpenStudy (anonymous):

is this some type of a rule or property we are following here

OpenStudy (xapproachesinfinity):

how about a trig sub that may be a good alternative

OpenStudy (xapproachesinfinity):

there is not rule just algebra we set a sub for our 1+y^2 to get a much better integrand that we can easily integrate

OpenStudy (xapproachesinfinity):

try trig sub make x=tantheta

OpenStudy (xapproachesinfinity):

i guess that would be faster and better

OpenStudy (anonymous):

can show me the solution please

OpenStudy (xapproachesinfinity):

i did not do the solution i'm just trying to give some alternatives you have to work it yourself

OpenStudy (xapproachesinfinity):

it has some work to it!

OpenStudy (anonymous):

i literally confused i am not good with this part of integration i was hoping for easier and understandavle approach

OpenStudy (xapproachesinfinity):

eh it is not gonna be that easy it needs some work

OpenStudy (xapproachesinfinity):

i just tried the trig sub turns out bad \[\int \csc\alpha\sec^2 \alpha d\alpha \] i chose \[y=\tan \alpha \] after this i'm inclined to integration by parts

OpenStudy (anonymous):

i am good at partial differentiation and ordinary too but integration is the most difficult one

OpenStudy (anonymous):

can you tell me a site where i can find example similar to this question please

OpenStudy (xapproachesinfinity):

if the answer that you want here http://www.wolframalpha.com/input/?i=int+%28sqrt%281%2By%5E2%29%2Fy%29dy

OpenStudy (xapproachesinfinity):

you have to do the same to right hand side with the difference of negative sign

OpenStudy (xapproachesinfinity):

looks like the solution will be accomplished by an integration by parts set u=1/y du=-1/y^2 dv=sqrt{1+y^2} v=int sqrt{1+y^2} try to work on it more you might get something

OpenStudy (anonymous):

ok ill try lets see :) thanks

OpenStudy (xapproachesinfinity):

no matter what you are required to do IBP

OpenStudy (xapproachesinfinity):

no problem

OpenStudy (xapproachesinfinity):

here something this guys did which the same thing i tried too above \[\int \csc \alpha \sec^2 \alpha d\alpha \] https://answers.yahoo.com/question/index?qid=20090211222753AACuIJB

OpenStudy (xapproachesinfinity):

it again needs IBP lol

OpenStudy (anonymous):

:)

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