- #1
whatisreality
- 290
- 1
Homework Statement
Find the eigenvalues of the matrix
##
\left( \begin{array}{cc}
3 & -1.5\\
-1.5 & -1\\
\end{array} \right)
##
It's probably a really stupid mistake, but the answer I get doesn't match the answer from wolfram alpha's eigenvalue calculator... always a bad sign.
Homework Equations
The Attempt at a Solution
The characteristic equation is:
(3-λ)(-1-λ) -##\frac{9}{4}## = 0
→ λ2-2λ - ##\frac{21}{4}## = 0
Using the quadratic formula,
λ = ##\frac{2 \pm \sqrt{4 - (4\times -\frac{21}{4})}}{2}##
= ##1 \pm \sqrt{25}##
= 6 or -4.
But apparently, I should be getting -1.5 and 3.5 . I have checked it so many times to see where I've gone wrong! What's the mistake??