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Jeff Miller: Earliest Uses of Various Mathematical Symbols
This site from Gulf High School explores the earliest uses of various mathematical symbols, words, and terms. A very interesting site.
Interactive Mathematics
Interactive Mathematics: Roots and Radicals
Here you'll find information on radicals: notation, symbols, and laws for simplifying. The information is brief, but easy to follow.
Wolfram Research
Wolfram Mathworld: Vinculum
A brief description of the viniculum, a part of the radical sign, notation for repeating decimals, distance between two points, and more.