Let f(x,y)=yx+yf(x,y) = \frac{y}{x+y}f(x,y)=x+yy. Find the first-order partial derivative ∂f∂x\frac{\partial f}{\partial x}∂x∂f.
−y(x+y)2-\frac{y}{(x+y)^2}−(x+y)2y
y(x+y)2\frac{y}{(x+y)^2}(x+y)2y
x(x+y)2\frac{x}{(x+y)^2}(x+y)2x
−x(x+y)2-\frac{x}{(x+y)^2}−(x+y)2x