- #1
TheSodesa
- 224
- 7
Homework Statement
[tex]
A = \begin{bmatrix}
2 & 1 & 0\\
0& -2 & 1\\
0 & 0 & 1
\end{bmatrix}
[/tex]
Homework Equations
The Attempt at a Solution
The spectrum of A is [itex] \sigma (A) = { \lambda _1, \lambda _2, \lambda _3 } = {2, -2, 1 } [/itex]
I was able to calculate vectors [itex]v_1[/itex] and [itex]v_3[/itex] correctly out of the vectors on the following page:
http://www.wolframalpha.com/input/?i=eigenvectors+of+{{2,1,0},{0,-2,1},{0,0,1}}
However, [itex]v_2[/itex] is giving me a headache. Using [itex] \lambda _1[/itex] to solve [itex]A - \lambda _1 I_3[/itex] gives me the matrix
[tex]
\begin{bmatrix}
\stackrel{a}{0} & \stackrel{b}{1} & \stackrel{c}{0}\\
0 & -4 & 1\\
0 & 0 & -1
\end{bmatrix}
\stackrel{rref}{=}
\begin{bmatrix}
\stackrel{a}{0} & \stackrel{b}{1} & \stackrel{c}{0}\\
0 & 0 & 1\\
0 & 0 & 0
\end{bmatrix}
[/tex]
In my head this would produce a zero eigenvector since
[tex]\begin{cases} b = 0 \\ c = 0 \\ (a = ?) \end{cases}[/tex]
This is of course nonsense. I'm probably interpreting the row-reduced matrix wrong, but what is it exactly that I'm not understanding? Does it have something to do with the fact that on every row a = 0?