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## Homework Statement

Let ABCD be a convex cyclic quadrilateral. Prove that

[tex]|AB-CD|+|AD-BC| \geq 2|AC-BD|[/tex]

## Homework Equations

## The Attempt at a Solution

First, isn't a cyclic quadrilateral always convex?

http://en.wikipedia.org/wiki/Cyclic_quadrilateral