ODE question - Integrating factor

[Pyroadept]

Homework Statement

Find all solutions of the equation:

y' = (2y)/(t.logt) = 1/t, t > 0

Homework Equations

Integrating factor I = exp(\intp(x)dx)

where y' + p(x)y = q(x)

The Attempt at a Solution

Hi everyone, here's what I've done so far:

Let p(t) = -2/(t.logt)

I = exp(\int((-2)/(t.logt))dt)

Factoring out the -2, consider \int1/(t.logt)dt

Use integration by parts:
u = 1/logt
du = -(logt)^-2.(1/t).dt

dv = (1/t)dt
v = logt

\intu.dv = uv - \intv.du

I end up with:

\int1/(t.logt)dt = 1 + \int1/(t.logt)dt

which gives me 0 = 1, which is clearly wrong.

But I can't see where I'm going wrong! I've done it five times now and I keep getting the same answer. Can anyone see where I'm going wrong or suggest another way of solving the problem?

Thanks for any help

 

[vela]

Try the substitution u=log t.

 

[vela]

You didn't do anything wrong when you integrated by parts. If you were evaluating definite integrals, the first term would drop out since you'd get 1-1=0. With the indefinite integrals, the paradoxical result arises because you've neglected the constant of integration.