设z=ln tan(y/x),求d(z)
问题描述：
设z=ln tan(y/x),求d(z)
答
z=ln tan(y/x)dz=d(ln tan(y/x)=tan(y/x)^(-1)[D(tan(y/x))/Dy]dy+tan(y/x)^(-1)[Dtan(y/x)/Dx]dx=tan(y/x)^(-1)(1+y^2/x^2)x^（-1）dy-tan(y/x)^(-1)(1+y^2/x^2)x^（-2）ydx