Mathematics
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OpenStudy (pawanyadav):
The solution of differential equation..
(x^2-y^2)dx +2xy dy=0
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OpenStudy (samigupta8):
Is the ans
1/2 ( y/x)^2=ln(c/x)
OpenStudy (xapproachesinfinity):
that's and exact equation
OpenStudy (loser66):
No, it is not,kid
OpenStudy (xapproachesinfinity):
why nit?
OpenStudy (loser66):
\(\partial M/\partial y=-2y\neq \partial N/\partial x= 2y\)
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OpenStudy (pawanyadav):
Yes , that equation is not right
OpenStudy (loser66):
So, you have to find \(\mu (x)\) or \(\mu (y)\) or \(\mu(xy)\) to have is exact
I worked on it, \(\mu (x)=1/x^2\) works well
OpenStudy (xapproachesinfinity):
yes, i miss that minus
OpenStudy (samigupta8):
Sorry ! I didn't take that 2 into consideration..
OpenStudy (loser66):
@Pawanyadav use (1/x^2) to multiple into both sides and then solve as usual
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OpenStudy (pawanyadav):
I do the same but can't reach the answer
OpenStudy (loser66):
Show your work, please.
OpenStudy (samigupta8):
I got this
y^2+x^2=cx
OpenStudy (xapproachesinfinity):
yeah old man is right
OpenStudy (pawanyadav):
I got logx= log (1+ (y/x)^2)+c
Whats next
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OpenStudy (xapproachesinfinity):
so what is the problem here, you made it exact
OpenStudy (samigupta8):
Not log x ..
It has to be log (1/x)
OpenStudy (xapproachesinfinity):
and solved it?
OpenStudy (loser66):
kid, then solve for f(x,y)
OpenStudy (xapproachesinfinity):
yes i know old man, I was talking to the poster
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OpenStudy (loser66):
kid, take over, please :)
OpenStudy (loser66):
@samigupta8 you got it right
OpenStudy (xapproachesinfinity):
\[(1-\frac{y^2}{x^2})dx+2\frac{y^2}{x}dy=0\]
OpenStudy (xapproachesinfinity):
which one did you integrate
OpenStudy (pawanyadav):
@samigupta how its log (1/x)
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OpenStudy (xapproachesinfinity):
that supposed to have only y not y^2
OpenStudy (samigupta8):
I got these equations
v/2 + xdv/dx +1/2v=0
So now u take all v terms on left side and x terms on right..
Solve it u will get the desired ans
OpenStudy (samigupta8):
v is y/x here
OpenStudy (xapproachesinfinity):
\[f(x,y)=\int 1-\frac{y^2}{x^2}dx=x+y^2/x+h(y)=c\]
OpenStudy (loser66):
Then, take derivative of the above result w.r.t y
it is = 2y/x +h'(y)
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OpenStudy (xapproachesinfinity):
yeah i know, just looking for something
OpenStudy (loser66):
Ok, kid, please, give him step by step. (Whole thing, please).
OpenStudy (pawanyadav):
On dividing by x^2 dx,we got
(1-(y/x)^2)=-2(y/x)y'
Now put y=tx
I got
(1-t^2)/-2t=t+x(dt/dx)
OpenStudy (pawanyadav):
Then
(t^2-1)/2t -t=x(dt/dx)
OpenStudy (xapproachesinfinity):
one second i will write the procedure
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OpenStudy (pawanyadav):
Finally
dx/x=(-2t/(1+t^2))dt
On integrate
-logx =log (1+t^2)+c
OpenStudy (pawanyadav):
Thanks ,, finally I got it
OpenStudy (pawanyadav):
Thanks old man and kid ..your method is little difficult..
OpenStudy (xapproachesinfinity):
OpenStudy (xapproachesinfinity):
what method are you using ?
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OpenStudy (pawanyadav):
Its all above..
OpenStudy (xapproachesinfinity):
yeah don't get, just tell me the name, i will check on it
OpenStudy (pawanyadav):
Homogenisation of equation
OpenStudy (xapproachesinfinity):
oh i see
OpenStudy (pawanyadav):
First convert to homogeneous equation than solve by variable separable form
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OpenStudy (xapproachesinfinity):
so you get the solution i wrote
OpenStudy (xapproachesinfinity):
yeah i have seen that before just don;t recall the whole procedure now
OpenStudy (pawanyadav):
No ,I can't open this page
OpenStudy (xapproachesinfinity):
it a word document
OpenStudy (pawanyadav):
OK ..I'll get i
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OpenStudy (xapproachesinfinity):
OpenStudy (xapproachesinfinity):
i made it a PDF
OpenStudy (pawanyadav):
Thanks , now I can opeopen
OpenStudy (pawanyadav):
I never solve any questions like this before
OpenStudy (loser66):
bravo, kid