MHB Solve Integral w/ Change of Variable Technique

[Stumped1]

How would I apply the change of variable technique to solve the integral
$$\int x\frac{2x}{1000^2}e^{-(x/1000)^2}dx$$

w/ out the $$x$$ I used
$$u=(x/1000)^2$$ , and $$du=2x/1000^2$$

Now, I am calculating $$E(x)$$, and now sure how to deal w/ the extra $$x$$.

Thanks for any help!

 

[Aryth1]

How would I apply the change of variable technique to solve the integral
$$\int x\frac{2x}{1000^2}e^{-(x/1000)^2}dx$$

w/ out the $$x$$ I used
$$u=(x/1000)^2$$ , and $$du=2x/1000^2$$

Now, I am calculating $$E(x)$$, and now sure how to deal w/ the extra $$x$$.

Thanks for any help!

The key is that substitution works both ways.

First, you let $u = \left(\frac{x}{1000}\right)^2$. So, what does that make $x$ equal to?