Originally Posted by

**Warrenx** Hey There,

My question involves the u-substitution rule for calculus. I do not understand it intuitively, and am relying purely on a mechanical recital, so I do not understand what happens to the "du"?

here is an example of my confusion:

$\displaystyle \int $$\displaystyle (x^2)$$\displaystyle (2x)$dx

= $\displaystyle \int $$\displaystyle u$du

= (x^2)/2 + C

so I set $\displaystyle u = x^2$ and $\displaystyle du = 2xdx$.

But where does the "du" go? It always seems to disappear, but I am not good enough at mathematics to understand why.

Thanks for your input.

-Warren