# Help with integration

1. Apr 29, 2009

### confused88

1. The problem statement, all variables and given/known data
Can someone please help me with integration of x(e^(-x-theta)) Thank you. My working is shown below

3. The attempt at a solution
u = x, du = 1 dx, dv = e^(-x-theta)) v = e^-x+theta+1 / theta + 1

the rest can be seen in the attachment. Can you please check it out, it would be greatly appreciated.Thanks

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• ###### integration.jpg
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2. Apr 29, 2009

### JG89

The attachment is pending approval so I can't see it.

Use the substitution $$u = -x - \theta \Rightarrow x = -(u+\theta) \Rightarrow dx = -du$$. So our integral is now $$\int (u + theta)e^u du$$.

Now use integration by parts.

3. Apr 29, 2009

### confused88

ohhh wow thanks a lot!!

4. Apr 29, 2009

### HallsofIvy

Staff Emeritus
The first thing I would do is write $e^{-x- \theta}= e^{-x}e^{-\theta}$ and factor out the $e^{-\theta}$. Your integral is just $e^{-\theta}\int xe^{-x}dx$ which can be done by integration by parts.