"Chances and Risks of Heuristic Reasoning: Some Examples using Derive" Johann Wiesenbauer Institut fuer Algebra und Diskrete Mathematik, Technische Universitaet Wien Wiedner Hauptstrasse 8-10 Vienna, Austria, A-1040 Austria E-mail:j.wiesenbauer@tuwien.ac.at Unlike everyday life in mathematics it is not sufficient that a certain statement is true in many cases or is derived on the grounds of "plausible" assumptions, but what is needed here is an exact proof. On the other hand, if such a proof is either not known or too difficult for classroom teaching, it may be a good idea to use heuristic reasoning instead. Some examples of this kind are given using Derive which clearly show the chances but also the risks in this field.