對一已知函數(shù)的導(dǎo)函數(shù)進(jìn)行求導(dǎo),所得函數(shù)叫做原函數(shù)的二階導(dǎo)數(shù),對二階導(dǎo)數(shù)再次進(jìn)行求導(dǎo),所得函數(shù)叫做原函數(shù)的三階導(dǎo)數(shù),同理可得對一函數(shù)求導(dǎo)多次所得函數(shù)即為該函數(shù)的多階導(dǎo)數(shù)。