Question

Find the characteristic polynomial of A. Use x for the variable in your polynomial.You do not need to factor your polynomial. A = [0 0 1] [ 4 -3 4] [-2 0 -3] 1. haracteristic polynomial of A is ____________?

Answer 1

Answer:  The required characteristic polynomial of the given matrix A is $x^3+6x+11x+6=0.$

Step-by-step explanation:  We are given to find the characteristic polynomial  of the following 3 × 3 matrix A  with unknown variable x :

$A=\left[\begin{array}{ccc}0&0&1\\4&-3&4\\-2&0&-3\end{array}\right].$

We know that

for any square matrix M, the characteristic polynomial is given by

$|M-xI|=0,$ where I is an identity matrix of same order as M.

Therefore, the characteristic polynomial of matrix A is

$|A-xI|=0\\\\\\\Rightarrow \left|\left[\begin{array}{ccc}0&0&1\\4&-3&4\\-2&0&-3\end{array}\right]-x\left[\begin{array}{ccc}1&0&0\\0&1&0\\0&0&1\end{array}\right]\right|=0\\\\\\\Rightarrow \left|\left[\begin{array}{ccc}-x&0&1\\4&-3-x&4\\-2&0&-3-x\end{array}\right] \right|=0\\\\\\\Rightarrow -x(3+x)^2+1(0-6-2x)=0\\\\\Rightarrow  (x+3)(-3x-x^2-2)=0\\\\\Rightarrow (x+3)(x^2+3x+2)=0\\\\\Rightarrow x^3+6x+11x+6=0.$

Thus, the required characteristic polynomial of the given matrix A is $x^3+6x+11x+6=0.$