If xy=yxx^y = y^xxy=yx, what is dydx\frac{dy}{dx}dxdy in terms of xxx and yyy?
\frac{y(y-x\ln y)}{x(x-y\ln x)}
\frac{y(x\ln y - y)}{x(y\ln x - x)}
\frac{y\ln y - x}{x\ln x - y}
\frac{y}{x}