Got Homework?
Connect with other students for help. It's a free community.
Here's the question you clicked on:
 0 viewing

This Question is Closed

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
start by factoring
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
then break apart in to two pieces then integrate term by term
 2 months ago

Elsa213 Group TitleBest ResponseYou've already chosen the best response.0
erm.... integral 4x/(1+x^2) = I Let 1+x^2 = t ...........(1) > 2x = dt/dx > 2x dx = dt ...........(2) Now I = integral 2 [2x dx / (1+x^2) ] = integral 2 [dt / t ] since from (2) = 2 [integral dt / t ] = 2 (ln t) +c = 2 ln(1+x^2) + c We have integral 1/t dt = ln t +c Therefore I = 2 ln(1+x^2) +c where ln is log to the base e https://answers.yahoo.com/question/index?qid=20110416060345AAVswO7
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
@Elsa213 i am pretty sure that is some other answer to some other question
 2 months ago

Elsa213 Group TitleBest ResponseYou've already chosen the best response.0
it was just an example
 2 months ago

cutelilgirl Group TitleBest ResponseYou've already chosen the best response.0
log  (2x+1)(2x1)  ??
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
log a.b=loga +logb then integrate each at a time
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
now \[\int \log(2x+1)dx+\int (2x1)dx\]
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
you forgot log lol
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
then you should be done because you should have the integral of the log memorized
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
so i did \[\int \log(2x+1)dx+\int \log(2x1)dx\]
 2 months ago

cutelilgirl Group TitleBest ResponseYou've already chosen the best response.0
the answer given is : x log  4x^21  1/2 log  (2x1)/(2x+1)  .. will i get this answer this way ?
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
yes continue this way
 2 months ago

cutelilgirl Group TitleBest ResponseYou've already chosen the best response.0
ok thanks @xapproachesinfinity and @satellite73
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
you should know what is int logxdx
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
i have no idea when you integrate you will get something then using the properties of the log you can change it in to many different forms don't get married to the answer in the book
 2 months ago

cutelilgirl Group TitleBest ResponseYou've already chosen the best response.0
because this exercise was about the problems of integral dx / (a^2_x^2) type
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
i would say this integral looks nothing like that at all
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
satellite you assumed that the expression will take positive values only you need the absolute value theere
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
i would say this integral looks nothing like that at all === is this to my reply^_^
 2 months ago

cutelilgirl Group TitleBest ResponseYou've already chosen the best response.0
yes the  4x^2 1  was there
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
i would say \[\int \log(4x^21)dx\] looks nothing like \[\int \frac{dx}{a^2x^2}\]
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
yes i doesn't :)
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
it*
 2 months ago

cutelilgirl Group TitleBest ResponseYou've already chosen the best response.0
or dx/x^2a^2
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
\[\int \log(x)dx=x\log(x)x\] so \[\int \log(2x+1)dx=\frac{1}{2}\left((2x+1)\log(2x1)(2x+1)\right)\] by a mental u sub second part is similar
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
@satellite73 , any reason why you took off absolute values?
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
damn typo \[\int \log(2x+1)dx=\frac{1}{2}\left((2x+1)\log(2x+1)(2x+1)\right)\]
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
or if you prefer \[\frac{1}{2}(2x+1)(\log(2x+1)1)\]
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
laziness is all that and the stupid \(+ c\) got omitted as well
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
but you excluded the negative values?
 2 months ago

ganeshie8 Group TitleBest ResponseYou've already chosen the best response.0
why wolfram is giving this mess http://www.wolframalpha.com/input/?i=%5Cint+log%28abs%284x%5E21%29%29
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
wolfram is crazy hehe
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
i say the absolute value cannot be taken off. as we are excluding negative interval here
 2 months ago

satellite73 Group TitleBest ResponseYou've already chosen the best response.1
wolfram gave that mess because of the sign problem here it is neater http://www.wolframalpha.com/input/?i=\int+log%284x^21%29
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
\(\Large \rm\color{midnightblue}{\int log(2x+1)(2x1)dx=\int log2x+1dx+\\ \int log2x1dx}\)
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
Integration by parts should even work for the first way this expression appears
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
integration by parts will be needed polynomial division partial fractions look like they are needed as well
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
i agree. i looks that the answer would look much simpler
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
x/(2x1)(2x+1) partial fraction here
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
the other part is good xlog4x^21
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
Whenever I see something that looks like \[\int\limits_{}^{}1 \cdot \ln(f(x)) dx \] one of my first instincts it to go with the integration by parts (assuming f>0) \[=x \ln(f(x))\int\limits_{}^{}x \frac{f'(x)}{f(x)} dx\]
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
so far it looks nice to me
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
where did you get that @xapproachesinfinity ?
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
dw:1408559618618:dw
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
from by part integration
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
this now going to that expression she wrote as the answer!
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
I don't see where that integral comes from
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
i wonder if you forget f' on top dw:1408559852906:dw
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
u=log(4x^21) ===> du=1/4x^21 dv=1 ====> v=x may be there is an error lol
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
derivative of ln(f) is equal to f'/f
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
yup you are right forgot that xD
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
it should be what you wrote above
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
@cutelilgirl are you still there?
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
8x^2/4x^21
 2 months ago

cutelilgirl Group TitleBest ResponseYou've already chosen the best response.0
yes but this seems a little beyond me :(
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
have you talked about integration by parts?
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
that is the only way i know how to do this problem
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
so i assume you have had it mentioned in class
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
is that a correct assumption
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
can't do partial fraction here
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
do you know how to evaluate \[\int \ln(x) dx ]
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
\[\int\limits_{}^{} \ln(x) dx\]
 2 months ago

myininaya Group TitleBest ResponseYou've already chosen the best response.1
If you don't I can show you that may help you seeing this more simple integral evaluated first
 2 months ago

xapproachesinfinity Group TitleBest ResponseYou've already chosen the best response.0
we need another integration by part? i guess
 2 months ago
See more questions >>>
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.