Find the solution to this Differential Equation

rodolfomz
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Homework Statement



Find the solution to ## \frac{dy}{dx} = yLn(y + 1) ##

Homework Equations



## \frac{dy}{dx} = yLn(y + 1) ##


The Attempt at a Solution



## \frac{dy}{dx} = yLn(y + 1)##

## \frac{dy}{yLn(y + 1)} = dx ##

but then i can't integrate, any help?
 
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rodolfomz said:

Homework Statement



Find the solution to ## \frac{dy}{dx} = yLn(y + 1) ##

Homework Equations



## \frac{dy}{dx} = yLn(y + 1) ##


The Attempt at a Solution



## \frac{dy}{dx} = yLn(y + 1)##

## \frac{dy}{yLn(y + 1)} = dx ##

but then i can't integrate, any help?
Using a substitution (u = ln(y + 1)) I was able to get to this integral:
$$\int \frac{du}{u} + \int \frac{du}{u(e^u + 1)}$$
The first integral is very simple. The second might be amenable to another substitution, but I didn't go any further.
 
thats what I have

## ∫\frac {dy}{y*ln(y+1)}=∫dx ##
changing variables
## u=ln(y+1) ; du=\frac{dy}{y+1} ##

##\int \frac{e^u*du}{(u)*(e^u -1)} = x ##
which is the same as

##\int \frac{du}{u}*\frac{e^u}{e^u-1} = x##

and then resolving by parts dv= du/u and u=e^u/e^u-1

##\frac{e^u}{e^u-1}+\int \frac{ln(u)*e^udu)}{(e^u-1)^2}##

im stuck here
 
rodolfomz said:

Homework Statement



Find the solution to ## \frac{dy}{dx} = yLn(y + 1) ##

Homework Equations



## \frac{dy}{dx} = yLn(y + 1) ##


The Attempt at a Solution



## \frac{dy}{dx} = yLn(y + 1)##

## \frac{dy}{yLn(y + 1)} = dx ##

but then i can't integrate, any help?

I doubt there is an elementary antiderivative. Where did this problem come from?
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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