Nice book on integrals [duplicate]
Solution 1:
Here are some reference sources:
- Inside Interesting Integrals by Paul J. Nahin
- A Treatise on Integral Calculus Volume 1 and Volume 2 by Joseph Edwards
- Superhuman Integration Techniques by Andre Kessler
- Integration: The Feynman Way
- Wikipedia: Differentiation Under The Integral Sign
- sos440's blog
Solution 2:
Irresistible Integrals by George Boros and Victor Moll is a fantastic book for all sorts of interesting approaches to integrals.