Cut The Knot
This website contains a very large collection of interactive activities created by the idiosyncratic Alexander Bogomolny to highlight elegant and powerful features of mathematics. Many aspects of secondary school mathematics are involved as well as many mathematical elements that are not part of the school curriculum. As CTK is a very extensive collection of several hundred applets, no choices will be ‘typical’. Equations of the straight line, Riemann Sums, and Polygonal Numbers illustrate three different possibilities, but you will find many others with other selections. To see the philosophy underpinning the collection, read the author’s manifesto, which is also accessible on each applet page.

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