The matrix \(B\) is defined by $$ B=\left(\begin{array}{ccc} -3 & -1 & 0 \\ 5 & 2 & 1 \\ -5 & 5 & -4 \end{array}\right) $$ (a) Calculate the eigenvalues of \(B\). (b) Calculate the eigenvectors of \(B\).

Short Answer

Expert verified
Based on the steps explained above, we calculated the eigenvalues of matrix \(B\) to be \(1, 2i, -2i\). After substituting each eigenvalue back into the equation \((B-\lambda I)X=0\), where X is the eigenvector and I is the identity matrix, we found the corresponding eigenvectors \(X_1 = \left(\begin{array}{c} 1 \\ -2 \\ 2 \end{array}\right), X_2 = \left(\begin{array}{c} 1 \\ i \\ 1-i \end{array}\right), X_3 = \left(\begin{array}{c} 1 \\ -i \\ 1+i \end{array}\right)\).

Step by step solution

01

Calculate the characteristic equation

To find the eigenvalues, we must first calculate the characteristic equation given by the determinant of \((B-\lambda I)\), which is $$ \text{det}(B-\lambda I) = \text{det}\left(\begin{array}{ccc} -3-\lambda & -1 & 0 \\\ 5 & 2-\lambda & 1 \\\ -5 & 5 & -4 -\lambda \end{array}\right) $$
02

Calculate the eigenvalues

Now, we find the determinant of the resulting matrix to form a polynomial equation in terms of \(\lambda\): $$ \text{det}(B-\lambda I) = (-3-\lambda)((2-\lambda)(-4-\lambda) - 5) + (-1)(5 - 5(\lambda + 4)) = (\lambda-1)(\lambda^2+4) $$ It can be seen that the eigenvalues are \(\lambda_1 = 1\) and \(\lambda_2 = 2i\), \(\lambda_3 = -2i\).
03

Calculate the eigenvectors for λ = 1

We substitute the eigenvalue \(\lambda_1 = 1\) back into the equation \((B-\lambda I)X=0\): $$ \left(\begin{array}{ccc} -3-1 & -1 & 0 \\\ 5 & 2-1 & 1 \\\ -5 & 5 & -4-1 \end{array}\right) \cdot \left(\begin{array}{c} x_{1} \\\ x_{2} \\\ x_{3} \end{array}\right) = \left(\begin{array}{c} 0 \\\ 0 \\\ 0 \end{array}\right) $$ $$ \left(\begin{array}{ccc} -4 & -1 & 0 \\\ 5 & 1 & 1 \\\ -5 & 5 & -5 \end{array}\right) \cdot \left(\begin{array}{c} x_{1} \\\ x_{2} \\\ x_{3} \end{array}\right) = \left(\begin{array}{c} 0 \\\ 0 \\\ 0 \end{array}\right) $$ Now we solve this system of linear equations to find one non-trivial eigenvector associated with \(\lambda_1 = 1\). We can get the eigenvector \(X_1 = \left(\begin{array}{c} 1 \\ -2 \\ 2 \end{array}\right)\).
04

Calculate the eigenvectors for λ = 2i and λ = -2i

Since the other eigenvalues are complex conjugates (\(\lambda_2 = 2i\) and \(\lambda_3 = -2i\)), we can find one eigenvector for the complex eigenvalue and then take its complex conjugate to find the eigenvector for the conjugate eigenvalue. We substitute the eigenvalue \(\lambda_2 = 2i\) back into the equation \((B-\lambda I)X=0\): $$ \left(\begin{array}{ccc} -3-2i & -1 & 0 \\\ 5 & 2-2i & 1 \\\ -5 & 5 & -4 - 2i \end{array}\right) \cdot \left(\begin{array}{c} x_{1} \\\ x_{2} \\\ x_{3} \end{array}\right) = \left(\begin{array}{c} 0 \\\ 0 \\\ 0 \end{array}\right) $$ Now we solve this system of linear equations to find one eigenvector associated with \(\lambda_2 = 2i\). We can find the eigenvector \(X_2 = \left(\begin{array}{c} 1 \\ i \\ 1-i \end{array}\right)\). To find the eigenvector associated with \(\lambda_3 = -2i\), we take the complex conjugate of \(X_2\): \(X_3 = \left(\begin{array}{c} 1 \\ -i \\ 1+i \end{array}\right)\). The eigenvectors of matrix \(B\) are: $$ X_1 = \left(\begin{array}{c} 1 \\ -2 \\ 2 \end{array}\right), X_2 = \left(\begin{array}{c} 1 \\ i \\ 1-i \end{array}\right), X_3 = \left(\begin{array}{c} 1 \\ -i \\ 1+i \end{array}\right) $$

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