Go backward to This is Not the Fallacy

Go up to 1=2: A Proof using Beginning Algebra

Go forward to This is the Fallacy

Switch to graphical version (better pictures & formulas)

Go to University of Toronto Mathematics Network Home Page

The distributive law says that x(y+z) = xy + xz for all numbers x, y, and z, and the factorization 2 a^2 - 2 ab = 2 (a^2 - ab) is simply an application of this to the particular case x=2, y=a^2, and z = -ab.

Writing a^2 - ab = 1(a^2 - ab) is legitimate since multiplying any number by 1 leaves the number unchanged.

Why don't you go back to the list of steps in the proof and see if you can identify which one is wrong, now that you know it isn't this one?

This page last updated: May 26, 1998

Original Web Site Creator / Mathematical Content Developer: Philip Spencer

Current Network Coordinator and Contact Person: Joel Chan - mathnet@math.toronto.edu

Navigation Panel: Previous | Up | Forward | Graphical Version | U of T Math Network Home