Commonly, if M^E for a binary system has a single sign, then the partial properties M̅^E₁  and M̅^E₂ have the same sign as M^E over the entire composition range. There are occasions, however, where the M̅^E_i may change sign even though M^E has a single sign. In fact, it is the shape of the M^E vs. x₁ curve that determines whether the M̅^E_i change sign. Show that a sufficient condition for M̅^E₁ and M̅^E₂ to have single signs is that the curvature of M^E vs. x₁ have a single sign over the entire composition range.