Calculate the spectral radius of $\begin{equation}A= \begin{pmatrix} 1 &1\\ 2 &1 \end{pmatrix} \end{equation} $
My understanding is spectral radius is maximum modulus of the largest eigenvalue of $A$
eigenvalues are $1+\sqrt2$ and $1-\sqrt2$
So, $\rho(A)=1+\sqrt2$
But in one research article $\rho(A)=\frac{1+\sqrt2}{2+\sqrt2}=\frac{1}{\sqrt2}$
Can Someone catch my mistake?
Thank in advanced.