Determine the value of $\lambda \in \mathbb{R}$ for which each list of vectors is linear dependent.
(a) $((\lambda,-1,-1),(-1, \lambda,-1),(-1,-1, \lambda))$ as a subset of $\mathbb{R}^{3}$.
(b) $\sin 2(x), \cos (2 x), \lambda$ as a subset of $\mathcal{C}(\mathbb{R})$.