2.I 6C6 \mathrm{C} \quad

Linear Mathematics
Part IB, 2001

Show that right multiplication by A=(abcd)M2×2(C)A=\left(\begin{array}{ll}a & b \\ c & d\end{array}\right) \in M_{2 \times 2}(\mathbb{C}) defines a linear transformation ρA:M2×2(C)M2×2(C)\rho_{A}: M_{2 \times 2}(\mathbb{C}) \rightarrow M_{2 \times 2}(\mathbb{C}). Find the matrix representing ρA\rho_{A} with respect to the basis

(1000),(0100),(0010),(0001)\left(\begin{array}{ll} 1 & 0 \\ 0 & 0 \end{array}\right),\left(\begin{array}{ll} 0 & 1 \\ 0 & 0 \end{array}\right),\left(\begin{array}{ll} 0 & 0 \\ 1 & 0 \end{array}\right),\left(\begin{array}{ll} 0 & 0 \\ 0 & 1 \end{array}\right)

of M2×2(C)M_{2 \times 2}(\mathbb{C}). Prove that the characteristic polynomial of ρA\rho_{A} is equal to the square of the characteristic polynomial of AA, and that AA and ρA\rho_{A} have the same minimal polynomial.