Wednesday, February 12, 2014

solve the differential equation : ylnx - xy' = 0

ylnx - xy' = 0


First we will
rewrite the equations.


ylnx =
xy'


==> ylnx = x
*dy/dx


In solving differential equation, out first priority
is to isolate x an y terms on different sides.


Then we will
multiply both sides by dx and divide by
xdy


==> lnx/x) dx =
dy/y 


Now let us integrate both
sides:


==> intg (lnx/x) dx = intg
dy/y


Let u= lnx


==> du
= 1/x  dx


==> x du =
dx


==> intg u/x * xdu = ln
y


==> intg u du = ln
y


==> ln y =  u^2 /2 +
C


Now subsitute with u= ln
x


==> ln y = (lnx)^2 /2  +
C


==> y= e^(1/2)(lnx)^2 +
C

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