设z=u^v,u=2+sin(xy),v=x-2y,求δz/δx,δz/δy

kuaidi.ping-jia.net  作者:佚名   更新日期:2024-08-24
设二阶偏导数连续的函数z=f(u,v),u=xy,v=x^2-y^2,求δz/δx,δz/δy,最好有详细的步骤

z=f(u,v), u=xy, v=x^2-y^2
du/dx=y, du/dy=x
dv/dx=2x, dv/dy=-2y
dz/dx=dz/du*du/dx+dz/dv*dv/dx
=df/du*y+df/dv*2x
dz/dy=dz/du*du/dy+dz/dv*dv/dy
=df/du*x-df/dv*2y

δz/δx=(δz/δu)*(δu/δx)+(δz/δv)*(δv/δx)
=((e^u)*sinv)*y+((e^u)*cosv)*1
=(e^xy)*[ysin(x+y)+cos(x+y);
δz/δy=(δz/δu)*(δu/δy)=(δz/δv)*(δv/δy)
=((e^u)*sinv)*x+((e^u)*cosv)*1
=(e^xy)*[xsin(x+y)+cos(x+y);

简单计算一下即可,答案如图所示



即z=e^ [ln(2+sinxy) *(x-2y)]
那么求偏导数得到
δz/δx=z *δ[ln(2+sinxy) *(x-2y)]/δx
=z *[y* cosxy/(2+sinxy) *(x-2y) +ln(2+sinxy)]

δz/δy=z *δ[ln(2+sinxy) *(x-2y)]/δy
=z *[x *cosxy/(2+sinxy) *(x-2y) -2ln(2+sinxy)]

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