Eigenvalues and eigenvectors of $$$\left[\begin{array}{cc}1 & 1\\1 & 1\end{array}\right]$$$

Find the eigenvalues and eigenvectors of $$$\left[\begin{array}{cc}1 & 1\\1 & 1\end{array}\right]$$$.

Start from forming a new matrix by subtracting $$$\lambda$$$ from the diagonal entries of the given matrix: $$$\left[\begin{array}{cc}1 - \lambda & 1\\1 & 1 - \lambda\end{array}\right]$$$.

The determinant of the obtained matrix is $$$\lambda \left(\lambda - 2\right)$$$ (for steps, see determinant calculator).

Solve the equation $$$\lambda \left(\lambda - 2\right) = 0$$$.

The roots are $$$\lambda_{1} = 2$$$, $$$\lambda_{2} = 0$$$ (for steps, see equation solver).

These are the eigenvalues.

Next, find the eigenvectors.

• $$$\lambda = 2$$$

  $$$\left[\begin{array}{cc}1 - \lambda & 1\\1 & 1 - \lambda\end{array}\right] = \left[\begin{array}{cc}-1 & 1\\1 & -1\end{array}\right]$$$

  The null space of this matrix is $$$\left\{\left[\begin{array}{c}1\\1\end{array}\right]\right\}$$$ (for steps, see null space calculator).

  This is the eigenvector.

• $$$\lambda = 0$$$

  $$$\left[\begin{array}{cc}1 - \lambda & 1\\1 & 1 - \lambda\end{array}\right] = \left[\begin{array}{cc}1 & 1\\1 & 1\end{array}\right]$$$

  The null space of this matrix is $$$\left\{\left[\begin{array}{c}-1\\1\end{array}\right]\right\}$$$ (for steps, see null space calculator).

  This is the eigenvector.

Eigenvalue: $$$2$$$A, multiplicity: $$$1$$$A, eigenvector: $$$\left[\begin{array}{c}1\\1\end{array}\right]$$$A.

Eigenvalue: $$$0$$$A, multiplicity: $$$1$$$A, eigenvector: $$$\left[\begin{array}{c}-1\\1\end{array}\right]$$$A.