# Nonlinear DE reduction

1. Jun 23, 2012

### sunrah

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

$\ddot{y} = - \dot{y} - y -sin(y)$

2. Relevant equations
3. The attempt at a solution
to reduce the order I need to find a solution y1. it seems to me the only obvious solution is y1 = 0 but i can't use this to do a reduction can i

2. Jun 23, 2012

### Infinitum

Hi sunrah!

You should be able to reduce the given DE to first order by substituting $\frac{dy}{dx}= t$

3. Jun 23, 2012

### sunrah

indeed, thank you!

4. Jun 23, 2012

### Infinitum

I hope you didn't write $$\frac{d^2y}{dt^2} = t'$$

5. Jun 23, 2012

### sunrah

i used
$\frac{d^{2}y}{dx^{2}} = \frac{dt}{dx}\frac{dy}{dy} = t\frac{dt}{dy}$

6. Jun 23, 2012

### Infinitum

Yep, perfect!

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