In mathematics , the differential coefficient of a function `` f '' ( `` x '' ) is what is now called its derivative `` df '' ( `` x '' ) / `` dx '' , the ( not necessarily constant ) multiplicative factor or `` coefficient '' of the differential `` dx '' in the differential `` df '' ( `` x '' ) .
The former `` differential coefficient '' of a function `` f '' ( `` x '' ) is now called its derivative `` df '' ( `` x '' ) / `` dx '' . It is the ( not necessarily constant ) multiplicative factor or `` coefficient '' of the differential `` dx '' in the differential `` df '' ( `` x '' ) .