In Green's theorem, \( \oint_C (x^2y dx + x^2 dy) = \iint_R f(x,y) dx dy \), where C is the boundary described counter clockwise of the triangle with vertices (0, 0), (1, 0), (1, 1) and R is the region bounded by a simple closed curve C in the x-y plane, then \( f(x,y) \) is equal to: