{x=x(u,v),y=y(u,v), z=z(u,v),
(u,v)∈D,
(xyz)=(x(u,v)y(u,v)z(u,v))=r(u,v)=x(u,v)i+y(u,v)j+z(u,v)k.
S=∬D|[r′u(u,v),r′v(u,v)]|dudv.
z=f(x,y), (x,y)∈D. ( x,y) r=r(x,y)=xi+yj+f(x,y)k.
r′x(x,y)=i+f′x(x,y)k, r′y(x,y)=j+f′y(x,y)k,
[r′x(x,y),r′y(x,y)]=|ijk10f′x(x,y)01f′y(x,y)|=−f′x(x,y)i−f′y(x,y)j+k.
|[r′x(x,y),r′y(x,y)]|=1+(f′x(x,y))2+(f′y(x,y))2,
S=∬D1+(f′x(x,y))2+(f′y(x,y))2dxdy.
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