Identify which of the following differential equations is separable.
dydx=x+y\frac{dy}{dx} = x + ydxdy=x+y
dydx=xy\frac{dy}{dx} = xydxdy=xy
dydx=xy\frac{dy}{dx} = \frac{x}{y}dxdy=yx
dydx=sin(x+y)\frac{dy}{dx} = \sin(x+y)dxdy=sin(x+y)