arctan(y/x)对y求导此处x、y均为独立的函数,对y求导可将x看成常数[arctan(y/x)]'={1/[1+(y/x)^2]}*(y/x)'={1/[1+(y/x)^2]}*1/x=x/(x^2+y^2)对xdx/(x^2+y^2)求积分对x积分可将y看成常数∫xdx/(x^2+y^2)=1/2∫dx...