3、
z=xln(xy)
az/ax=ln(xy)+x/(xy)·y
=ln(xy)+1
a^2z/ax^2=1/(xy)·y
=1/x
a^3z/(ax^2ay)=0
az/zx=ln(xy)+1
a^2z/(axay)=1/(xy)·x
=1/y
a^3z/(axay^2)=-1/y^2
z=xln(xy)
az/ax=ln(xy)+x/(xy)·y
=ln(xy)+1
a^2z/ax^2=1/(xy)·y
=1/x
a^3z/(ax^2ay)=0
az/zx=ln(xy)+1
a^2z/(axay)=1/(xy)·x
=1/y
a^3z/(axay^2)=-1/y^2
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