1.對(duì)于二元函數(shù)z=f(x,y),若
存在,則稱
為f(x,y)在點(diǎn)(x
0,y
0)處對(duì)x的偏導(dǎo)數(shù),記為f′
x(x
0,y
0);若
存在,則稱
為f(x,y)在點(diǎn)(x
0,y
0)處對(duì)y的偏導(dǎo)數(shù),記為f′
y(x
0,y
0).已知二元函數(shù)z=f(x,y)=x
2-2xy+y
3(x>0,y>0),則f
x′(x
0,y
0)+f
y′(x
0,y
0)的最小值為
.