Quadrature

Quadrature, derived from Latin quadrare, is a term with various meanings:

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• Quadrature amplitude modulation (QAM), a modulation method of using both a carrier wave and a 'quadrature' carrier wave that is 90° out of phase with the main carrier
• Quadrature of the circle (also squaring the circle), in geometry, the problem of constructing a square and circle of equal area, impossible using only an unmarked straight-edge and compass
• Numerical integration, in mathematics, summing in quadrature means summing the squares of numbers, then taking the square root, as used in error analysis
• In astronomy, quadrature occurs when two celestial bodies appear 90° apart from one another as viewed from a third celestial body. As an example, the Moon and the Sun are in quadrature with respect to the Earth when the Moon is in its exact first quarter or last quarter phases. The symbol for astronomical quadrature is a hollow square.