对x求偏导时,y是常数,变量只有分母有,那么z=y(x^2+y^2)^(-1/2),所以əz/əx=y(x^2+y^2)^(-3/2) *(-1/2) *2x=-xy/(x^2+y^2)^(3/2)对y求偏导时,x是常数,分子和分母都有变量那么əz/əy=(x^2+y^2)^(-1/2)+y(x^2+y^2)^(-3/2) *(-1/2) *2y=1/(x^2+y^2)^(1/2)-y^2/(x^2+y^2)^(3/2)=x^2/(x^2+y^2)^(3/2)