Stage: 4 and 5 Challenge Level: 
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The idea came from a discussion between Toni Beardon and Bryan Dye (webmaster of MathsNet ) and the program has been written by Elizabeth Ayer.
Mathematical reasoning & proof. Inequality/inequalities. Quadratic equations. Patterned numbers. Visualising. Manipulating algebraic expressions/formulae. Generalising. Long problems. Number theory. Interactivities.
Published May 2001.
Copyright © 2007. University of Cambridge. All rights reserved.
NRICH is part of the family of activities in the Millennium Mathematics Project, which also includes the Plus and Motivate sites.
email: nrich@damtp.cam.ac.uk
