If you take a look at WolframAlpha, or other computer algebraic system, you will find that it is able to do symbolic manipulation like real humans.
For example, if you type in an integral, it can show you step by step on how to solve the integration.
What are the algorithms behind all this?
Best Answer
The algorithms behind symbolic integration (due to Liouville, Ritt, Risch, Bronstein et al.) are discussed in prior questions here, e.g. the transcendental case and algebraic case.
For general references on symbolic computation see any of the standard texbooks, e.g. Geddes et al. Algorithms for computer algebra, Grabmeier et al: Computer algebra handbook,von zur Gathen: Modern computer algebra, and Zippel: Effective polynomial computation, and many other books. See also the Journal of Symbolic Computation and various conferences: SIGSAM ISSAC, EUROCAL, etc.