Problem solving for linear algebra's matrix R

Question

i found "U" but failed to find "R". What I did is add row3 to row2, then divide by pivots, which gave me my "R".

i thought that;s how its done, why did i fail it. How is it done?

Answer 1

You left out a pivot. You should have $$ \begin{bmatrix} 1&0&-1\\ 0&1&-1 \end{bmatrix} $$

Answer 2

Reduced row echelon form requires that the pivots (the left-most non-zero entry of every row) must be 1. In $U$, you already have this in the bottom row. All that is needed is to divide the top row by 3.