Find the scalar product (a.b) and the vector product $(\mathbf{a} \times \mathbf{b})$, when
(a) $\mathbf{a}=\mathbf{i}+2 \mathbf{j}-\mathbf{k}, \mathbf{b}=2 \mathbf{i}+3 \mathbf{j}+\mathbf{k}$
(b) $\mathbf{a}=2 \mathbf{i}+3 \mathbf{j}+4 \mathbf{k}, \mathbf{b}=5 \mathbf{i}-2 \mathbf{i}+\mathbf{k}$