y = cos(x + y)dy/dx = dcos(x + y)/d(x + y) · d(x + y)/dx,链式法则dy/dx = - sin(x + y) · (1 + dy/dx)dy/dx = - sin(x + y) - sin(x + y) · dy/dxdy/dx · [1 + sin(x + y)] = - sin(x + y)dy/dx = - sin(x +...