Ask your own question, for FREE!
Mathematics 20 Online
OpenStudy (anonymous):

Solve the Initial Value Problem

OpenStudy (anonymous):

\[x^{2}\frac{ dy }{ dx}=\frac{ 4x^{2}-x-2 }{ (x+1)(y+1) } ,y(1)=1\]

OpenStudy (anonymous):

please write step by step, im sorry

OpenStudy (loser66):

\[(y+1) dy =\frac{4x^2-x-2}{x^2(x+1)}dx \] Ok?

OpenStudy (anonymous):

i get that

OpenStudy (loser66):

integral both sides. That's it

OpenStudy (anonymous):

okay please bear with me, as it can get crazy

OpenStudy (anonymous):

im working on it

OpenStudy (loser66):

I guess so, but that the steps after getting the answer, replace initial value to get value of C, then plug back

OpenStudy (anonymous):

okay give me 10000 seconds please

OpenStudy (anonymous):

\[\int\limits_{}^{}\frac{ 4x ^{2}-x-2 }{ x ^{2}(x+1) }dx\]

OpenStudy (anonymous):

it has already gotten crazy

OpenStudy (loser66):

use partial fraction, friend

OpenStudy (anonymous):

could you do a quick refresher, my apologies as it has been last last year doing this

OpenStudy (loser66):

\[\frac{4x^2-x-2}{x^2(x+1)}=\frac{A}{x+1}+\frac{B}{x}+\frac{C}{x^2}\] solve for A, B, C you have A = 3, B =1, C =-2 so, the integral becomes \[\int( \frac{3}{x+1}+\frac{1}{x}-\frac{2}{x^2})dx\] then take integral each term to get the answer

OpenStudy (anonymous):

light BULB! thank you!

OpenStudy (loser66):

ok

OpenStudy (anonymous):

im sorry for making you work that out

OpenStudy (loser66):

np.

OpenStudy (anonymous):

nevermind!

OpenStudy (anonymous):

how do you integrate the y part?

OpenStudy (loser66):

do as usual, = \(\dfrac{y^2}{2}+y\)

OpenStudy (anonymous):

i got 3ln(x+1)+lnx+2/x for the other side thank you

OpenStudy (loser66):

+ C

OpenStudy (anonymous):

so i got y^2x/2+y=3ln(x+1)+lnx+2/x+c

OpenStudy (loser66):

yes, I think so

OpenStudy (loser66):

no, y^2 /2, not y^2x/2

OpenStudy (anonymous):

you're right my bad

OpenStudy (anonymous):

and then solve for y?

OpenStudy (loser66):

solve for C

OpenStudy (loser66):

replace initial value y(1) =1 to solve for c

OpenStudy (anonymous):

so plug 1 in for y? im sorry

OpenStudy (loser66):

first off, you have to solve for y . I am sorry, it's not easy but we have an outlet there y^2 + 2y - 2( the whole thing from the left hand side) =0 . This is a quadratic equation, you solve for y, so, y = ....( 2 values) then, plug x =1 into this y and the whole thing = 1 because y(1) =1 to solve for c

OpenStudy (loser66):

because from the differential equation above, your answer is y^2/2 +y , not just y, So, you have to solve for y , and then calculate the initial value base on the latest y

OpenStudy (loser66):

gotta go. be back later.

OpenStudy (anonymous):

thanks

OpenStudy (loser66):

hey, you see, wolfram solves this problem exactly our way, hehehe http://www.wolframalpha.com/input/?i=x^2%28dy%2Fdx%29%3D%284x^2-x-2%29%2F%28%28x%2B1%29%28y%2B1%29%29

OpenStudy (anonymous):

how does wolfram jump from x^2(dy/dx)=(4x^2-x-2)/((x+1)(y+1) to the long equation with y(x)?

OpenStudy (loser66):

don't you scrool up? it solves the problem at the beginning of the problem, drag the bar up to see the very first step

OpenStudy (anonymous):

i don't have an account for that

OpenStudy (anonymous):

i don't see it

OpenStudy (loser66):

OpenStudy (loser66):

can you read it?

OpenStudy (anonymous):

yes i can

OpenStudy (anonymous):

but how do they get from 1/2 y^2+y=3ln(x+1)+lnx+2/x+c to the longer equation with y(x)

OpenStudy (loser66):

hey, don't be panicked. I told you , it's a quadratic , see -1 at the end of each y the equation is \[y^2 +2y -(6ln(x+1)+lnx +\frac{2}{x}+C) =0\]

OpenStudy (loser66):

so, \[ y = \frac{-2\pm\sqrt {2^2-4*1*(the~~whole~bracket)}}{2}\]

OpenStudy (loser66):

got it?

OpenStudy (anonymous):

it's a lot to take in

OpenStudy (loser66):

yes, but we are on the right track, right? lalalaala from these, plug x =1 and y =1 into them to have C

OpenStudy (loser66):

It is the beginning of the semester, right?

OpenStudy (anonymous):

sorry!

OpenStudy (anonymous):

because there is a lot for you to delete.

OpenStudy (anonymous):

yes

OpenStudy (anonymous):

jamal is a boy name in america

OpenStudy (anonymous):

con trai

OpenStudy (anonymous):

not yet :( school first

OpenStudy (anonymous):

that's good, son

OpenStudy (anonymous):

tại sao tên của dì loser66?

OpenStudy (loser66):

How do you understand the word of "Loser"?? 66 is my born year

OpenStudy (anonymous):

cảm ơn rất nhiều! nghe có vẻ rất tốt đẹp

OpenStudy (loser66):

Please, speak English!! Your Vietnamese is ridiculous as my English. hehehe

OpenStudy (anonymous):

you said that sentence very well! hahaha

OpenStudy (loser66):

And don't forget correct my English, please

OpenStudy (loser66):

including vocabulary.

OpenStudy (anonymous):

And don't forget to correct my English, please

OpenStudy (anonymous):

It's getting late now and I have class tomorrow morning. Thank you for helping me with math, it was nice getting you to know you! I will see you soon when I have new questions, which I will. Good night!

OpenStudy (anonymous):

you can send it from here

OpenStudy (loser66):

ok

OpenStudy (loser66):

OpenStudy (anonymous):

Thank you very much!

Can't find your answer? Make a FREE account and ask your own questions, OR help others and earn volunteer hours!

Join our real-time social learning platform and learn together with your friends!
Can't find your answer? Make a FREE account and ask your own questions, OR help others and earn volunteer hours!

Join our real-time social learning platform and learn together with your friends!