已知函数F(u,v,ω)可微,F’u(0,0,0)=1,F’v(0,0,0)=2,F’ω(0,0,0)=3,函数z=f(x,y)由F(2x—y+3z,4x2一y2+z2,xyz)=0确定,且满足f(1,2)=0,则f’x(1,2)=________.

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问题 已知函数F(u,v,ω)可微,F’u(0,0,0)=1,F’v(0,0,0)=2,F’ω(0,0,0)=3,函数z=f(x,y)由F(2x—y+3z,4x2一y2+z2,xyz)=0确定,且满足f(1,2)=0,则f’x(1,2)=________.

选项

答案—2

解析 记G(x,y,z)=F(2x—y+3z,4x2一y2+z2,xyz)=0,则当z=f(x,y)时,即G(x,y,z)=G[x,y,f(x,y)]=0,等式两边对x求偏导,有G’x·1+G’y·0+G’z·f’x(x,y)=0.所以f’x(x,y)=一,即

当(x,y,z)=(1,2,0)时,则(u,v,ω)=(0,0,0),故
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