Inscriptible Quadrilateral: An Illustration

The applet below illustrates the theorem of Pitot.

For a quadrilateral ABCD circumscribed around a circle the sums of opposite sides are equal:

AB + CD = BC + DA.

This applet requires Sun's Java VM 2 which your browser may perceive as a popup. Which it is not. If you want to see the applet work, visit Sun's website at http://www.java.com/en/download/index.jsp, download and install Java VM and enjoy the applet.

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What if applet does not run?

The commonly given proof of the converse contains a subtle flaw which is not at all simple to fix. But an additional proof smoothes the wrinkles.

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