- #1
bobmerhebi
- 38
- 0
Homework Statement
Use the appropriate substitution to solve the following D.E.: -ydx + (x + [tex]\sqrt{}xy[/tex])dy = 0
Homework Equations
y = ux
The Attempt at a Solution
y = ux implies dy = udx + xdu
so -xudx + (x + x[tex]\sqrt{}u[/tex])(udx + xdu) =0
we then get after some simplificaion: xu[tex]\sqrt{}u[/tex] dx + x2 (1 + [tex]\sqrt{}u[/tex])du = 0
so (1/x).u[tex]\sqrt{}u[/tex]dx + (1 + [tex]\sqrt{}u[/tex])du = 0
hence dx/x + du/(u[tex]\sqrt{}u[/tex]) + du/u = 0
now we have after integrating: lnx + lnu - 2/[tex]\sqrt{}u[/tex] = c1
substituting bk u= y/x we have: ln x + ln (y/x) - 2[tex]\sqrt{}x[/tex]/[tex]\sqrt{}y[/tex] = c1
ln x + ln y - lnx - 2[tex]\sqrt{}x[/tex]/[tex]\sqrt{}y[/tex] = c1
so ln y - 2[tex]\sqrt{}x[/tex]/[tex]\sqrt{}y[/tex] = c1
here i got stuck. i couldn;t continue although i know that the answer should be : 4x = y(ln|y| - c)2
need help in this please. my process is right isn't it? how should i continue?