Unfortunately, the TI-84+ series calculators aren't capable of doing those kinds of calculations. The TI-89 calculators, however, are, because of a built-in Computer Algebra System, which allows them to also solve equations and the like.
Perhaps there is a program or shell somewhere that... Perhaps this : http://www.ticalc.org/archives/files/fileinfo/368/36857.html might be along the lines of what you're looking for? I agree that this option should be standard for all TI-8x calculators.
