Consider the spin-echo pulse sequence shown in Fig. 7.14 (c) on page 164. By considering the evolution of the operators x and 2zx, show that the coupling is refocused, and that, from the point of view of the evolution of these operators, the sequence is equivalent to a 180° pulse to the S spin.
Without detailed calculations, state what effect you expect sequence (c) to have on the evolution of the operators x and 2xz.