Eigenvalue of triangular matrix are elements in diagonal.
Now, consider the following matrix with eigenvalue $-5$ and $4$: $$\begin{bmatrix} -4 & 2 \\ 4 & 3 \\ \end{bmatrix}$$ Now if I do row operation $R_2\to R_2-(-R_1)$ and convert above matrix to following $$\begin{bmatrix} -4 & 2 \\ 0 & 5 \\ \end{bmatrix}$$ The eigenvalue of this is $-4$, $5$
First one is correct, what is wrong with the second one?