Given P = \(\begin{bmatrix}1 & 2\\2 & 3\end{bmatrix}\), find P\(^2\) - 4P - I where I is the identity matrix
A
\(\begin{bmatrix}1 & 0\\0 & 1\end{bmatrix}\)
B
\(\begin{bmatrix}0 & 0\\0 & 0\end{bmatrix}\)
C
\(\begin{bmatrix}-1 & 0\\0 & -1\end{bmatrix}\)
D
\(\begin{bmatrix}0 & 1\\1 & 0\end{bmatrix}\)
Verified Correct Answer: B.
Step-by-Step Mathematical Solution
Given the matrix
\(P = \begin{bmatrix} 1 & 2 \\ 2 & 3 \end{bmatrix},\)
we want to find \( P^2 - 4P - I \), where \( I \) is the identity matrix:
\(I = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}.\)
Calculate {\( P^2 \)}
\(P^2 = P \times P = \begin{bmatrix} 1 & 2 \\ 2 & 3 \end{bmatrix} \times \begin{bmatrix} 1 & 2 \\ 2 & 3 \end{bmatrix} = \begin{bmatrix} 5 & 8 \\ 8 & 13 \end{bmatrix}.\)
Calculate {\( 4P \)}
\(4P = 4 \times \begin{bmatrix} 1 & 2 \\ 2 & 3 \end{bmatrix} = \begin{bmatrix} 4 & 8 \\ 8 & 12 \end{bmatrix}\)
Calculate {\( P^2 - 4P \)}
\(P^2 - 4P = \begin{bmatrix} 5 & 8 \\ 8 & 13 \end{bmatrix} - \begin{bmatrix} 4 & 8 \\ 8 & 12 \end{bmatrix} = \begin{bmatrix} 5 - 4 & 8 - 8 \\ 8 - 8 & 13 - 12 \end{bmatrix} = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}\)
Calculate {\( P^2 - 4P - I \)}
\(P^2 - 4P - I = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} - \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} = \begin{bmatrix} 0 & 0 \\ 0 & 0 \end{bmatrix}\)
Thus, the result of \( P^2 - 4P - I \) is
\(\begin{bmatrix} 0 & 0 \\ 0 & 0 \end{bmatrix}\)
Source: Myschool Past Questions Archive (Record #70327)