"Once you've integrated"- that is after you have done the integration- there should no longer be a "dx" or "dy" in the expression!
#4
crador
94
11
As mentioned above dx just means "a little piece of x". So A dx is just the A times a little piece dx. Integrating means you do this many times, and add up the results. You can even do dx dy to have little squares, and other such things if you get clever!
I'm reviewing Meirovitch's "Methods of Analytical Dynamics," and I don't understand the commutation of the derivative from r to dr:
$$
\mathbf{F} \cdot d\mathbf{r} = m \ddot{\mathbf{r}} \cdot d\mathbf{r} = m\mathbf{\dot{r}} \cdot d\mathbf{\dot{r}}
$$