In mathematics, certain kinds of mistaken proof are often exhibited, and sometimes collected, as illustrations of a concept of **mathematical fallacy**. There is a distinction between a simple *mistake* and a *mathematical fallacy* in a proof: a mistake in a proof leads to an **invalid proof** just in the same way, but in the best-known examples of mathematical fallacies, there is some concealment in the presentation of the proof. For example the reason validity fails may be a division by zero that is hidden by algebraic notation. There is a striking quality of the mathematical fallacy: as typically presented, it leads not only to an absurd result, but does so in a crafty or clever way. Therefore these fallacies, for pedagogic reasons, usually take the form of spurious proofs of obvious contradictions. Although the proofs are flawed, the errors, usually by design, are comparatively subtle, or designed to show that certain steps are conditional, and should not be applied in the cases that are the exceptions to the rules.

The traditional way of presenting a mathematical fallacy is to give an invalid step of deduction mixed in with valid steps, so that the meaning of fallacy is here slightly different from the logical fallacy. The latter applies normally to a form of argument that is not a genuine rule of logic, where the problematic mathematical step is typically a correct rule applied with a tacit wrong assumption. Beyond pedagogy, the resolution of a fallacy can lead to deeper insights into a subject (such as the introduction of Pasch's axiom of Euclidean geometry). *Pseudaria*, an ancient lost book of false proofs, is attributed to Euclid.

Mathematical fallacies exist in many branches of mathematics. In elementary algebra, typical examples may involve a step where division by zero is performed, where a root is incorrectly extracted or, more generally, where different values of a multiple valued function are equated. Well-known fallacies also exist in elementary Euclidean geometry and calculus.

Read more about Mathematical Fallacy: Howlers, Multivalued Functions, Power and Root, Geometry

### Other articles related to "mathematical fallacy, fallacy":

**Mathematical Fallacy**- Geometry - Fallacy of The Isosceles Triangle

... The

**fallacy**of the isosceles triangle, from (Maxwell 1959, Chapter II, ยง 1), purports to show that every triangle is isosceles, meaning that two sides of the ... This

**fallacy**has been attributed to Lewis Carroll ...

### Famous quotes containing the words fallacy and/or mathematical:

“I’m not afraid of facts, I welcome facts but a congeries of facts is not equivalent to an idea. This is the essential *fallacy* of the so-called “scientific” mind. People who mistake facts for ideas are incomplete thinkers; they are gossips.”

—Cynthia Ozick (b. 1928)

“What is history? Its beginning is that of the centuries of systematic work devoted to the solution of the enigma of death, so that death itself may eventually be overcome. That is why people write symphonies, and why they discover *mathematical* infinity and electromagnetic waves.”

—Boris Pasternak (1890–1960)