求函数的所有二阶偏导数

如题所述

第1个回答  2016-04-16
Z = e^y cos(x-y)
Z'x = -e^y sin(x-y)
Z''xx = -e^y cos(x-y)
Z''xy = -e^ysin(x-y)+e^ycos(x-y)
= e^y [cos(x-y) - sin(x-y)]
Z'y = e^ycos(x-y) + e^ysin(x-y) = e^y[sin(x-y)+cos(x-y)]
Z''yy = e^y [sin(x-y)+cos(x-y)] + e^y [-cos(x-y) + sin(x-y)]
= 2 e^y sin(x-y)
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