Determine (f_xy) when (f(x, y) = 2y tan⁻¹ x/y).
a) (f_xy = -2y²/x²+y²)
b) (f_xy = 2x²/x²+y²)
c) (f_xy = 2xy/x²+y²)
d) (f_xy = -2xy/x²+y²)