## Elementary Linear Algebra 7th Edition

Multiply the first row by $2$ and add the result to the second row.
Given $$\left|\begin{array}{rr}{2} & {1} \\ {0} & {-1}\end{array}\right|=\left|\begin{array}{ll}{2} & {1} \\ {4} & {1}\end{array}\right|.$$ In the determinant in the left hand side, multiply the first row by $2$ and add the result to the second row, we get the determinant in the right hand side.