偏导的符号打不出，就用d代替了哈，函数就用Φ代替了哈~
z=Φ(x^2-y^2)
则dz/dx=Φ'(x^2-y^2)*2x
dz/dy=Φ'(x^2-y^2)*(-2y)
则dz/dx*y=dz/dy*(-x)=Φ'(x^2-y^2)*2xy
则dz/dx*y+dz/dy*x=0
选C
z=Φ(x^2-y^2)
则dz/dx=Φ'(x^2-y^2)*2x
dz/dy=Φ'(x^2-y^2)*(-2y)
则dz/dx*y=dz/dy*(-x)=Φ'(x^2-y^2)*2xy
则dz/dx*y+dz/dy*x=0
选C
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