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Coefficient, in Algebra, is the factor in a term by which the unknown quantity is multiplied. Thus in the terms 3x, ax, the coefficients are 3 and a. The term differential coefficient is applied in the higher calculus to represent the rate of change of one quantity with regard to another on which it depends. [Calculus.] In physics the term is frequently used. The coefficient of linear expansion of a substance for temperature means the amount of expansion that unit length of the substance undergoes when its temperature increases from 0° to 1° C. Similarly for expansion of areas and volumes. In electrical engineering the temperature coefficient of a metal is the proportional increase in its resistance per degree rise in temperature.