\(\mbox{For a }n \times n \mbox{ matrix A, }Det[c A] = c^n Det[A], c \in \mathbb{R} \\ \mbox{so for }n=4, c=2, Det[2a]=2^4 Det[A] = 16 Det[A] = 16 \times \dfrac 1 2 = 8\)
