Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 4 / 58 / b / iii

The third term is $2F(11)\cos [2\pi (x+y)]$. To reinforce a maximum at $(x_0,y_0)$ from the preceding table, its sign should beHence the direct-methods triplet relationship is $S(10)S(01)S(11)\simeq +1$ for the strong reflections under consideration. This maximizes constructive density at shared atomic positions. For weak or competing reflections the relation is probabilistic rather than an unconditional algebraic theorem.