Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

(a) -$\hat{j}$ (b) 0
(a) $\hat{i}\times (\hat{i}\times \hat{j})= \hat{i}\times (\hat{k})= -\hat{j}$ (b) $(\hat{i}\times \hat{j})\times \hat{k}= (\hat{k})\times \hat{k}= 0$