Which substitution turns dydx=x+yx−y\frac{dy}{dx} = \frac{x+y}{x-y}dxdy=x−yx+y into a separable equation?
y=vxy = vxy=vx
y=v+xy = v+xy=v+x
y=v/xy = v/xy=v/x
y=vx2y = vx^2y=vx2