z=arctanx/y + ln√(x^2+y^2)
编微分的符号打不出来,只有用d代替了
dz/dx=1/(1+(x/y)^2)*1/y +1/√(x^2+y^2) * 1/2√(x^2+y^2) * 2x
=y/(x^2+y^2)+x/(x^2+y^2)
=(x+y)/(x^2+y^2)
dz/dy=1/(1+(x/y)^2)*x*(-1/y^2) +1/√(x^2+y^2) * 1/2√(x^2+y^2) * 2y
=-x/(x^2+y^2)+y/(x^2+y^2)
=(y-x)/(x^2+y^2)
dz=(x+y)dx/(x^2+y^2)+(y-x)dy/(x^2+y^2)