若z = sin ( xy ) 则它的全微分dz =A:xcos (xy) B:(xdx+ydy) cos (xy) C:ycos (xy) D:(ydx+xdy) cos (xy)

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若z = sin ( xy ) 则它的全微分dz =A:xcos (xy)    B:(xdx+ydy) cos (xy)    C:ycos (xy)    D:(ydx+xdy) cos (xy)
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若z = sin ( xy ) 则它的全微分dz =A:xcos (xy) B:(xdx+ydy) cos (xy) C:ycos (xy) D:(ydx+xdy) cos (xy)
若z = sin ( xy ) 则它的全微分dz =
A:xcos (xy)
B:(xdx+ydy) cos (xy)
C:ycos (xy)
D:(ydx+xdy) cos (xy)

若z = sin ( xy ) 则它的全微分dz =A:xcos (xy) B:(xdx+ydy) cos (xy) C:ycos (xy) D:(ydx+xdy) cos (xy)
dz=cos(xy)ydx+cos(xy)xdy=(ydx+xdy)cos(xy),选D

z=sin(xy)
dz = cos(xy) .[ xdy+ydz]
ans:b

∂z/∂x=cos(xy)*y
∂z/∂y=cos(xy)*x
所以dz=ycos(xy)dx+xcos(xy)dy

dz=ycos(xy)dx+xcos(xy)dy