# Differential equation and initial value

1. Sep 23, 2009

### -EquinoX-

1. The problem statement, all variables and given/known data

[img=http://img3.imageshack.us/img3/3417/questionec.th.jpg]

2. Relevant equations

3. The attempt at a solution

I tried dividing both sides by (x^5+1), however the integration becomes really complex... can someone give me suggestions on how to do this?

2. Sep 23, 2009

### rock.freak667

put the -10x4y on the left side then divide by tr x5+1. Integrating factor it.

3. Sep 24, 2009

### -EquinoX-

that's what I did and then I need to integrate -10x^4/(x^5+1) dx right and then then to get the integrating factor is just e to the power of whatever the result of the integration is... however the integration is quite hard...

4. Sep 24, 2009

### rock.freak667

alright now, so

$$\int \frac{-10x^4}{x^5+1} dx$$

see how d/dx(x5+1)=5x4 ?

Can you use a substitution to make this integral easier?

5. Sep 24, 2009

### -EquinoX-

Okay say I solve the integral and then the integrating factor would be e to the power of this resulting integral right? so then what do I need to do next in order to solve for this problem?

6. Sep 24, 2009

### rock.freak667

right so for y'+P(x)y=Q(x), when you multiply by an integrating factor 'u', the left side becomes d/dx(uy) . That's why we multiply by u in the first place.

So you'll need to basically integrate uQ(x) w.r.t. x

7. Sep 24, 2009

### -EquinoX-

and then divide that by the integrating factor right?

8. Sep 24, 2009

### rock.freak667

yes you can if you feel the need to.

9. Sep 24, 2009

### -EquinoX-

what do you mean by if I need to? doesn't it always works like that?

10. Sep 24, 2009

### -EquinoX-

this now comes to:

$$\int \frac{x^2+5x-4}{x^5+1} e^{-2ln(x^5+1)} dx$$

I guess this can be simplified to:

$$\int \frac{x^2+5x-4}{(x^5+1)^3} dx$$

is this true?

how can I solve this such complex integration?

Last edited: Sep 25, 2009
11. Sep 25, 2009

### -EquinoX-

12. Sep 25, 2009

### rock.freak667

Re do your integrating factor as it was to integrate 10x4/(x5+1) not with the -ve sign.

13. Sep 25, 2009

### -EquinoX-

Integrating $$\frac{10x^4}{(x^5+1)}$$ the result I got is $$2ln(x^5+1)$$ and so the integrating factor is $$e^{2ln(x^5+1)}$$ which simplifies to $$(x^5+1)^2$$.

Then I do $$\int (x^2+5x-4)(x^5+1)$$ and the result of this integration I divide by $$(x^5+1)^2$$ which is the integrating factor. Is this the correct step to find the solution?

Please correct me if I am wrong.

Last edited: Sep 26, 2009
14. Sep 25, 2009

### rock.freak667

yes just integrate and divide, also don't forget the constant of integration

15. Sep 26, 2009

### -EquinoX-

by the constant of integration you mean the C right? The terms after integration that I found is very long.....