An interesting point when using Op-Amps: doing linear operations (addition/subtraction/multiplication by a scalar/integration/etc) is pretty easy (they are "linear devices").

Doing multiplication/division/exponentiation/etc is actually a little more difficult. Typically, they are done through log amplifiers[0], of which there are plenty of monolithic versions.

[0] http://www.analog.com/media/en/training-seminars/tutorials/M...