e^xy+tan(x+y)=2
e^xy(y+xdy/dx)+1/cos^2(x+y) * (1+dy/dx)=0
ye^xy+xe^xy *dy/dx +1/cos^2(x+y) +dy/dx *(1/cos^2(x+y))=0
ye^xy+1/cos^2(x+y)=-(xe^xy+1/cos^2(x+y))dy/dx
dy=-[ye^xy+1/cos^2(x+y)]/(xe^xy+1/cos^2(x+y)) * dx
e^xy+tan(x+y)=2,求dy
e^xy+tan(x+y)=2
e^xy(y+xdy/dx)+1/cos^2(x+y) * (1+dy/dx)=0
ye^xy+xe^xy *dy/dx +1/cos^2(x+y) +dy/dx *(1/cos^2(x+y))=0
ye^xy+1/cos^2(x+y)=-(xe^xy+1/cos^2(x+y))dy/dx
dy=-[ye^xy+1/cos^2(x+y)]/(xe^xy+1/cos^2(x+y)) * dx