Differential of a function

In calculus, the differential represents the principal part of the change in a function y = f ( x ) {\displaystyle y=f(x)} with respect to changes in the independent variable. The differential d y {\displaystyle dy} is defined by d y = f ′ ( x ) d x , {\displaystyle dy=f'(x)\,dx,} where f ′ ( x ) {\displaystyle f'(x)} is the derivative of f with respect to x {\displaystyle x} , and d x {\displaystyle dx} is an additional real variable (so that d y {\displaystyle dy} is a function of x {\displaystyle x} and d x {\displaystyle dx} ).

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