A Binary Operator Symbol Identification.

[BrockLee]

I am curious what the wikipedia page <http://en.wikipedia.org/wiki/Pythagorean_addition> is referring to when it qoutes that symbol " a Little X in a Circle ", It says and I qoute the binary operation a "that symbol" b = sqrt(a^2 + b^2), Pythagoreans Hypotenuse. Much abliged.

 

[micromass]

It's just a symbol to denote that particular addition. They draw a circle around it so you wouldn't confuse it with the regular +
The LaTeX code is \oplus if you want to know. Also, the $$\oplus$$ is more commonly used in vector spaces to denote the direct sum, which is a totally unrelated use.