Leibniz (Fraction) Notation
To do integration by substitution using Leibniz notation, we think of the derivative function as a fraction of infinitesimally small quantities du and dx. We change variables by manipulating these infinitesimal quantities.
The general strategy is pretty much the same as before:
- Change variables (substitute in u for some function of x).
- Put the original variable back (substitute the function of x back in for u).