Find the potential of the vector field f~ (x, y, z) = e xy/z (1 + xy z )~i + x 2 z ~j − x 2y z 2 ~k , and use the fundamental theorem for line integrals to evaluate z c f~ · d~r, where c is the straight line segment from (1, 1, 1) to (2, 2, 1). can one choose an arbitrary piece-wise smooth curve c with initial point (1, 1, 1) and terminal point (2, 2, 1) instead of the straight line segment?