A proof which can be accomplished using only real numbers (i.e., real analysis instead of complex analysis; Hoffman 1998, pp. 92-93).

Hoffman, P. The Man Who Loved Only Numbers: The Story of Paul Erdős and the Search for Mathematical Truth. New York: Hyperion, 1998.

Wells, D. The Penguin Dictionary of Curious and Interesting Numbers. Middlesex, England: Penguin Books, p. 22, 1986.

CITE THIS AS:

Weisstein, Eric W. "Elementary Proof." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/ElementaryProof.html