Basic differential equations, homogeneous method

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xy'-y =sqrt((x^2)+y(^2))
so by method of homogeneous equations I get arcsinh(y/x) = ln|x|+c but don't know what to do from there. the book suggests using sinhx = 1/2 (e^x - e^-x) but I don't know how to incorporate this. The answer should be y= (1/2) * (cx^2 - 1/c). How do you get this?

This is my work so far:
y'-(y/x) = sqrt (1+(y/x)^2)
since y=ux...
du/(sqrt(1+u^2) = dx/x
taking the antiderivatives gives
arcsinh(u) = ln|x|+c
where
arcsinh|y/x| = ln|x|+c
 
Last edited:
[itex]sinh^{-1}(\frac{y}{x}) = lnx + ln A[/itex] (I put c=lnA to make things simpler)
[itex]\Rightarrow sinh^{-1}(\frac{y}{x}) = lnAx[/itex]


[tex]\Rightarrow \frac{y}{x} = sinh(lnAx)[/tex]


and they said that


[tex]sinhX=\frac{e^X - e^{-X}}{2}[/tex]


So [itex]sinh(lnAx)[/itex] should make the equation

[tex]\frac{y}{x}=\frac{e^{lnAx}-e^{-lnAx)}}{2}[/tex]

Do you see how to continue from here?
 

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