Which of the following differential equations is separable?
dydx=x+y\frac{dy}{dx} = x + ydxdy=x+y
dydx=xy\frac{dy}{dx} = \frac{x}{y}dxdy=yx
dydx=x2+y2\frac{dy}{dx} = x^2 + y^2dxdy=x2+y2
dydx=sin(x+y)\frac{dy}{dx} = \sin(x+y)dxdy=sin(x+y)