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Home  >>  CBSE XII  >>  Math  >>  Differential Equations
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Show that the differential equation is homogeneous and solve\[y'=\frac{x+y}{x}\]

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1 Answer

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Solution: $y = x. logx + C.x$

Tool Box:

  • A differential equation of the form dy/d = F(x,y) is said to be homogenous if F(x,y) is a homogenous function of degree zero.
  • To solve equations of this type we substitute $y = vx and dy/dx = v + xdv/dx$

Step1.

$F(x,y) = (x+y)/x$
$F(kx,ky) = k(x+y)/kx = k^0.f(x,y)$
Hence $F(x,y)$ is a homogenous degree of zero.

Step2.

Using the information in the tool box, let us substitute $y = vx and dy/dx = v+xdv/dx.$
$v + x.dv/dx = (x+vx)/x$
Taking x as the common factor and cancelling we get
$v + x.dv/dx = 1 + v$
Bringing v from LHS to the RHS and cancelling wwe get $x.dv/dx = 1$

Step3. 

Seperating the variables we get, $dv = dx/x$

integrating on both sides we get, integration of v = integration of dx/x
i.e, $v= logx + C$

substituting for v
$y/x = logx + C$
Therefore, $y = x.logx + Cx$

This is the required solution for the differential equation.

 

answered Dec 24, 2012 by vijayalakshmi_ramakrishnans
edited Dec 24, 2012 by balaji.thirumalai
 

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