$\hat{i} \times(\hat{j} \times \hat{k})=?$

$\begin{aligned} & \hat{i} \times(\hat{j} \times \hat{k}) \\ = & \hat{i} \times \hat{i} \\ = & |\hat{i}||\hat{i}| \sin 0^{\prime} \\ = & 0\end{aligned}$